Look at the picture.
The formula for finding the sum of the measure of the interior angles is
(n - 2) · 180°
n - the number of sides
We have the pentagon → n = 5. Susbtitute:
(5 - 2) · 180° = 3 · 180° = 540°
Therefore
x = 540 - (140 + 120 + 96 + 112) = 540 - 468 = 72
a + x = 180°
Therefore a = 180° - 72° = 108°
Answer: a = 108°