Nine plus fifteen divide by five multiply by thirteen equal

PEMDAS. Parentheses, Exponents, Multiplication and Division, Addition and Subtraction. Go through your equation from left to right, checking for each one. When you find one, operate on it, and then start again from the beginning.

Any parentheses? Nope.

Any exponents? Nope.

We do have division. 15/5 = 3. That gives us 9+3x13=?.

Any parentheses? Nope.

Any exponents? Nope.

We do have multiplication. 3x13 = 39. That gives us 9+39=?

Any parentheses? Nope.

Any exponents? Nope.

Any multiplication or division? Nope.

Any addition? Yes. 9+39=48. 48=?

We are done now. The answer is 48.