#### Answer

4/5

#### Work Step by Step

In order to simplify a fraction, we must divide both the numerator (top of the fraction) and denominator (bottom of the fraction) by the same number. In order to simplify a fraction, divide the numerator and denominator by the greatest common factor of the two numbers. In this case, the greatest common factor of 12 and 15 is 3. Thus, we divide the numerator and denominator by 3 to obtain the simplified form of the fraction: 4/5.