Question 85428
distance = (rate)(time)

rate = {{{distance/time}}}

{{{20/t}}} = {{{15/t}}} + 9

Multiply by t:

t({{{20/t}}} = {{{15/t}}} + 9)
Cancel denominators:
20 = 15 + 9t
Subtract 15 from both sides:
5 = 9t
Divide both sides by 9:
5/9 = t

{{{20/(5/9)}}} = 20{{{{9/5}}}) = 36 MPH