Let's begin by listing out the information given to us:
m∠ABC = 3x + 3
m∠DEF = 5x - 33
From the question, m∠ABC & m∠DEF are identical (have same properties)
m∠ABC = m∠DEF
3x + 3 = 5x - 33
Put like terms together (add 33 - 3x to both sides)
3x - 3x + 3 + 33 = 5x - 3x - 33 + 33
36 = 2x; 2x = 36
x = 18