Question

What is the value of x in the equation 4x + 8y = 40, when y = 0.8?

Answer 1

$4x+8y=40\\\\ \ \ \ \ when\ y=0.8:\\\\4x+8\cdot0.8=40\\4x+6.4=40\ \ \ \ |subtract\ 6.4\\4x=40-6.4\\4x=33.6\ \ \ |:4\\\boxed{x=8.4}$

Answer 2

Now first of all we should plug in 0.8 to y .
now we have this simple equation: 4x+8.(0.8)=40
4x+6.4=40
4x=33.6
x=8.4  (hope it helps :) )