How do u solve the following equation: |r|=1

You're almost looking at the solution.  Almost.

If it only said  "  r = 1 ", then that would be the solution right there.

But it says "  | r | = 1 ", so there's a little more to it.

'r' can be either  +1  or  -1  and that equation will be a true statement.

So  +1  and  -1  are both solutions.

Given A =20000

T =9years