Answer
x=55
Work Step by Step
The same-side interior angles postulate tells us that $\angle4$ and $\angle7$ are supplementary.
$m\angle4+m\angle7=180\longrightarrow$ definition of supplementary
$70+2x=180\longrightarrow$ substitution
$2x=110\longrightarrow$ subtraction property of equality
$x=55\longrightarrow$ division property of equality