Question

Marika is training for a track race She starts by sprinting 100 yards . She gradually increases her distance , adding 4 yards a day for 21 days how far does she sprint on day 21 
using an=100+(n-1)4

Answer 1

For this case, you must use the given expression, taking into account that:
 n = number of days.
 We have then that for day 21, n = 21.
 Substituting we have:
 a21 = 100 + (21-1) * 4
 a21 = 180
 Answer: 
 she sprints 180 yards on day 21