To calculate: The calcium present in 1 cup of milk and in 1 cup of coo

Calculation:
Consider that Shenika had 3 cups of milk and 1 cup of cooked spinach for a total of 1140 mg of calcium. The next day, she had 2 cups of milk and ${\displaystyle 1\frac{1}{2}}$ cups of cooked spinach for a total of 960 mg of calcium.
Convert this problem into two system of equations.
Let the amount of calcium present in 1 cup of milk be x mg and the amount of calcium present in 1 cup of cooked spinach be y mg.
Shenika had 3 cups of milk and 1 cup of cooked spinach for a total of 1140 mg of calcium.
Now, this can be represented by a linear equation which is as follows,
${\displaystyle 3x+y=1140}$.....(1)
The next day, she had 2 cups of milk and ${\displaystyle 1\frac{1}{2}}$cups of cooked spinach for a total of 960 mg of calcium.
Now, this can be represented by a linear equation which is as follows,
${\displaystyle 2x+1.5y=960}$
Multiply with 10 to clear decimals of above equation.
${\displaystyle 20x+15y=9600}$......(2)
${\displaystyle 4x+3y=1920}$
So, the system of equation becomes as,
${\displaystyle 3x+y=1140}$
${\displaystyle 4x+3y=1920}$
Now, multiply the first equation with -3.
${\displaystyle -9x-3y=-3420}$
${\displaystyle 4x+3y=1920}$
Add these equations and solve for x.
${\displaystyle -9x+4x-3y+3y=-3420+1920}$
${\displaystyle —5x=-1500}$
${\displaystyle x=\frac{-1500}{-5}}$
${\displaystyle x=300}$
Substitute 300 for x in the (1) equation and solve for y.
${\displaystyle 3\left(300\right)+y=1140}$
${\displaystyle 900+y=1140}$
${\displaystyle y=1140-900}$
${\displaystyle y=240}$
Substitute the ordered pair in each equation to verify the system of equation.
Substitute ${\displaystyle (x,y)=(300,240)}$ in first equation.
${\displaystyle 3\cdot 300+240\stackrel{?}{=}1140}$
${\displaystyle 900+240\stackrel{?}{=}1140}$
${\displaystyle 1140=1140}$
The result is true.
Substitute ${\displaystyle (x,y)=(300,240)}$ in second equation.
${\displaystyle 4\cdot 300+240\stackrel{?}{=}1920}$
${\displaystyle 1200+720\stackrel{?}{=}1920}$
${\displaystyle 1920=1920}$
The result is true.
Therefore, the calcium present in 1 cup of milk is 300 mg and in 1 cup of cooked spinach is 240 mg.