Answer
$5$ GB.
Work Step by Step
Step 1. Let $x$ be the number of GB needed. For Data Plan A, we have $cost1=52+18x$, and for Data Plan B, we have $cost2=32+22x$.
Step 2. Letting $cost~1=cost~2$, we have $52+18x=32+22x$, $4x=20$ and $x=5$ GB.