You have two parallel lines crossed by a secant line. In this case, you have that the angles right side and down of the parallel lines are equal.
The algebraic expressions for such angles are:
9x - 7
7x - 3
Next, you equal the previoues expression (because those angles are equal) and solve for x, just as follow:
9x - 7 = 7x - 3 subtract 7x both sides and add 7 both sides
9x - 7x = - 3 + 7 simplify similar terms
2x = 4 divide by 2 boths sides
x = 4/2
x = 2
Hence, the value of x is x = 2