A quarter of the learners in a class have blond hair and two thirds of the learners have brown hair. The rest of the learners have black hair.

How many of the learners are there in the class if 9 of them have blond hair?

n = number of the learners in a class

A quarter of the learners in a class have blond hair means:

n / 4 of the learners in a class have blond hair

9 of the learners in a class have blond hair so:

n / 4 = 9

Multiply both sides by 4

n = 36