Answer:
$1200
Step-by-step explanation:
On an annual basis, Susie will be paying ($300×12) = $3600 the first year, and ($50×12) = $600 more each year after. The average rent over the 5-year period will be the rent in year 3, or $3600 +2×600 = $4800.
Susie's total rent for the period is ...
$4800×5 = $24,000
and Bailey's total commission will be ...
0.05 × $24,000 = $1200
_____
The sequence of annual rents is an arithmetic sequence with first term 3600 and common difference 600. The total of n terms of an arithmetic sequence will be ...
sum = (2·a1 +d(n -1))×(n/2)
= (2·3600 +600(5-1))(5/2) = 24000 . . . for n=5
This is the average term multiplied by the number of terms. When the number of terms is odd, the average term is the middle one (term 3 when there are 5 terms).
