You have two parallel lines crossed by a secant line p.
Then, due to the previous situation, you have that measure of angle ∠1 is equal to the measure of angle ∠2.
In order to determine the value of x, equal the algebraic expressions for angles ∠1 and ∠2, just as follow:
m∠1 = 7x
m∠2 = 5x + 30
m∠1 = m∠2
7x = 5x + 30 subtract 5x both sides
7x - 5x = 30 simplify like terms
2x = 30 divide by 2 both sides
x = 30/2
x = 15
Hence, the value of x is x = 15