To solve this formula for T, divide both sides of the original equation by PR:
I PRT
------ = --------- => T = I / (PR)
PR PR
Please note: Because the formula I = PRT involves neither addition nor subtraction, the final formula for T cannot involve either addition nor subtraction. That leaves:
T = I P/R
T= IPR
The second formula here is incorrect; we cannot solve I = PRT for T simply by rearranging the order of the variables. This leaves T = I P/R as a possible answer, but this answer does not agree with my T = I / (PR). Please double check to ensure that you have copied down the four possible answers correctly.
Answer:
Amount each friend pays for the gift = $20
Step-by-step explanation:
Market price of a gift = $70
The store manager takes $10 off the market price.
Marked down amount = $10
New cost price = Marked price - Marked down amount 
The cost of the gift is divided among three friends.
This means that the cost of gift which is $60 is divided by three to get each one's contribution in the gift.
∴ Amount each friend pays for the gift 
B. 10.1%
(2)(12)($88.18) ÷ [($1100)(18+1)]
(2,116.32) ÷ (20,900)
= 0.1012
= 10.1%