Complementary angles
Two angles are complementary when the sum of their measures is equal to 90°. Then if we have an angle with a measure of x° and another with a measure of y° and they are complementary we get the following:

Measures of A and B
We are told that A and B are complementary which means that their measures meet the following equation:

We also know that A is four times larger than B so we get:

Then if we replace A with 4B in the first equation we get:

Then we divide both sides by 5:

Then, if B is 18° A must be:

So A=72°. Then the answer is option D.