HELP QUICK IM FAILING Select the expression that represents the following statement: 6 times one fifth the sum of 13 and 7. (4 points)

a
6 x one fifth x (13 ÷ 7)

b
one fifth x (13 − 7) x 6

c
6 x one fifth x (13 x 7)

d
one fifth x (13 + 7) x 6

Martha is training for a duathlon, which includes biking and running. she knows that yesterday she covered a total distance of over 55.5 miles in more than than 4.5 hours of training. martha runs at a speed of 6 mph and bikes at a rate of 15.5 mph.