Okie, so they give you an equation with 2 variables. You know one which is y=6, but you do not know the other. So to solve this problem, you plug in the variable that you know and you solve for the other one.
x = ?
y = 6
5x + 4y = 39
5x + 4(6) = 39 Substitute the variable
5x + 24 = 39 Simplify
5x = 15 Subtract 24 from both sides
x = 3 Divide both sides by 5 to isolate x
B) x = 3
* if you wanna check your answer, just plug in all the factors and if the equation is true, then you are right
5(3) + 4(6) = 39
15 + 24 = 39 Yup, so the answer is correct
I hope this helps :-)
