It's D.30 because 600 divided by 20 is 30 or u can multiply 30 x 20 = 600.
There can be 2 ways. One is that the digits of the numerator and denominator are consecutive. And the other one is that either the numerator or denominator is a prime number.
I'm guessing that this one is another complementary angle, so the equation should be 90- 30= (THE ANSWER VARIABLE). Again, complementary angles add up to 90 degrees.
