Very urgent slope question

question: bill drove his car at a constant speed while on a trip. kevin drove his car at a different constant speed while on this same trip. the graph and the table show information about the trips bill and kevin took. which sentance correctly compares the rates bill and kevin drove on their trips?

choices:

a) bill drove at a rate that was 10 miles per hour slower than the rate kevin drove.

b) bill drove at a rate that was 10 miles per hour faster than the rate kevin drove.

c) bill drove at a rate that was 20 miles per hour slower than the rate kevin drove

d) bill drove at a rate that was 20 miles per hour faster than the rate kevin drove.