Anna’s age increased by 3 times her age, the result is 72

Anna’s age increased by 3 times her age, the result is 72.

Let a be Anna's age. We have:
a + 3a = 72

Combine like terms:
(1 + 3)a = 72
4a = 72

Type 4a = 72 into our calculator, and we get a = 18.