For this case we have the following equation:
[tex]A = \frac {1} {2} (a + x) * h[/tex]
We must clear the variable "x":
We multiply by 2 on both sides of the equation:
[tex]2A = (a + x) * h[/tex]
We divide by h on both sides of the equation:
[tex]\frac {2A} {h} = a + x[/tex]
We subtract "a" on both sides of the equation:[tex]\frac {2A} {h} -a = x[/tex]
Answer:[tex]x = \frac {2A} {h} -a[/tex]
