In 8 years kelly's age will be twice what it is now. How old is kelly?

In 8 years kelly's age will be twice what it is now. How old is kelly?

Let Kelly's age be a.

In 8 years means we add 8 to a:
a + 8

Twice means we multiply a by 2:
2a

The phrase will be means equal to, so we set a + 8 equal to 2a
a + 8 = 2a

To solve this equation, we type it in our math engine and we get:
a = 8

Evaluate a = 8 and check our work
8 + 8 ? 2(8)
16 = 16