Let X be the number of miles he rode the first day then
The rest is up to you!
darren went on holiday.in 5 days he rides his bike 120 miles.each day he rode 6 miles less than the previous day .how many miles did he ride each day ?.if he went on riding his bike 6 miles less each day,how far would he have ride altogether?
In your case n=5, d=-6, a= 120.
You can use the recurrent relation for the days in between:
with the terms same as above.
For the total use the formula for the sum of an arithmetic sequence:
with the terms the same as above