Answer:
x = 7
Explanation:
if A and B were parallel then
4x + 14 and 3x + 21 are alternate angles and are congruent , so
4x + 14 = 3x + 21 ( subtract 3x from both sides )
x + 14 = 21 ( subtract 14 from both sides )
x = 7
For A to be parallel to B then x = 7