Question 62783

Given
y = 4 - x --->(1)
3x + 4y = 21 --->(2)

Now substitue equation(1) in (2), we get

3x+ 4(4-x) = 21

3x + 16 -4x= 21 

16 -x = 21

Get all the numbers on one side, we get

16 -21 = x

-5 = x

Now substitue for x =-5 in equation(1), we get

y = 4 -(-5) = 4 + 5 = 9

Hence the value of x = -5 and y = 9