Question 100770
distance(d)=rate(r) times time(t) or d=rt;r=d/t and t=d/r

Let d=distance to work
And let r=his rate on Wednesday
Then r+12=his rate on Thursday

distance to work on Wed=rt=r*45 or 45r
distance to work on Thursday=rt=(r+12)*(45-9)=36(r+12)

distance to work on Wed=distance to work on Thu.  So our eq to solve is:

45r=36(r+12)  get rid of parens

45r=36r+432  subtract 36 from both sides
45r-36r=432  collect like terms

9r=432  divide both sides by 9

r=48mph--------------------rate on Wed
r+12=48+12=60mph---------------rate on Thu

d=rt=48*(3/4)=36 mi (Wed)(note:45 min=3/4 hr)--------------------Ans
d=rt=60*(3/5)=36 mi (thu)(note: 36 min=3/5hr)


Hope this helps--ptaylor