You rented a beach umbrella for 6 days. The first day was 20. Each day afterwards the cost dropped by 2 a day. What did you spend for the umbrella for all 6 days?

On the first day the cost is $20

Over the next 5 days the price decreased by 2

So, day 1 - $20

Day 2 - $18

Day 3 - $16

Day 4 - $14

Day 5 - $12

Day 6 - $10

We'll then add them all to find the total over 6 days

$20+$18+$16+$14+$12+$10 = $90

Over all six days, the total price is $90