Question

How do I answer this question on khan academy.

Answer 1

If
`b` is Ben's age and
`i` is Ishaan's age, then

• present day:
  `b=4i`
• 6 years ago:
  `b-6=6(i-6)`

Rewrite the second equation as

`b-6=6(i-6)\implies b-6=6i-36\implies b+30=6i`

Substitute
`b=4i` into this equation to solve for
`i`:

`b+30=6i\implies4i+30=6i\implies30=2i\implies i=15`

Then

`b=4i\implies b=4\cdot15=60`

So Ben is 60 years old now.