Answer:
[tex]2\; x[/tex] miles.
Step-by-step explanation:
What's the speed of car B?
[tex]v_B = v_a + x = 45 + x[/tex] miles per hour.
How far does each car travel in two hours?
[tex]s = v \cdot t[/tex].
How many miles further does car B travel in two hours than car A?
[tex]s_B - s_A = (90 + 2 \; x) - 90 = 90 - 90 + 2\; x = 2 \; x[/tex] miles.