Help me solve this d=rt problem

Question

Matt decides it's time to get in shape, so he goes out for a run. He runs for 60 feet before twisting his ankle. he then hobbles at a rate that is 8 feet/second slower than his running speed. the whole ordeal from when he leave home until he returns, last 20 seconds. what was matt's running speed AND what was matt's hobbling speed?

Answer 1

60=rt

60/r=t

60=(r-8)(20-t)

60=(r-8)(20-[60/r])

multiply both sides by r

60r=(r-8)(20r-60)

60r=20r²-160r-60r+480

20r²-220r+480-60r=0

20r²-280r+480=0

r²-14r+24=0

(r-12)(r-2)=0

r-12=0

r=12 feet per second (running)

r-8=4 feet per second (hobbling)