HOMEWORK HELP PLEASE

Question

For a certain bathtub, the cold water faucet can fill the tub in 12 minutes. Together, the cold and hot water faucets can fill the tub in 8 minutes. How long will the hot water faucet take to fill the tub alone? (rate of first + rate of second = rate of together) 

Answer 1

1/12 + 1/r = 1/8

multiply by 24r

2r + 24 = 3r

r = 24 minutes for the hot water faucet alone