Answer:
Alfonso bikes at 24 mph.
Step-by-step explanation:
going
t = 54/(r + 4)
coming
t = 30/(r - 4)
54/(r + 4) = 30/(r - 4) times are equal
54(r - 4) = 30(r + 4) product means/extremes
54r - 216 = 30r + 120 distribute
24r - 216 = 120 subtract 30r from both sides
24r = 336 add 216 to both sides
r = 14 divide both sides by 24