Adding interest rate to an amount

[Doingsomemath]

Hi, I don't know how to do this question. If you could help I would greatly appreciate.

Keith took out a loan of $50000 at a simple interest rate of 10% p.a. for 18 months.
a) How much interest did he have to pay?
b) How much did he have to pay back at the end.

 

[Doingsomemath]

Sorry, I've solved it now. Thanks!

 

[lue]

how did you solve it??