Question

3 batteries cost $5r and 8 folders cost $2r. Jason bought 6 batteries and 4 folders how much does he pay. Give answer in terms of r

Answer 1

6 = 2 *3
so 6 batteries cost 2 * cost of 3 batteries
which is 10 r
then 4 folders costs 1/2 as much as 8 folders
so 1 r
10 r + 1 r = 11 r

Answer 2

or...
cost of 1 battery = 5/3 r
cost of 1 folder = 2/8 r = r/4

cost of 6 batteries and 4 folders
= 6(5/3)r + 4(r/4) = 10r + r = 11r