Nina had 1/7 as many cakes to sell as Belle. The two friends decided to share the work evenly. To do that, Belle had to give 15 cakes to Nina. What was the total number of cakes the two friends had to sell?

Answer 1

b-15 = b/7 + 15
b = 35
so nina had 5, and together they had 40

check:
35-15 = 5+15

Answer 2

x = number of cakes Nina would have after getting the 15. Multiply that by 2 for both of them.

6/7x = 15

Answer 3

n = b/7
n + 15 = b - 15 or n = b - 30
so
b -30 =b/7
7 b - 210 = b
6 b = 210
b = 35
n = b - 30 = 5
35 + 5 = ?

Answer 4

number of cakes that Nina has = x
number of cakes that Belle has = 7x

Belle gives 15 to Nina, Belle now has 7x - 15
Nina has x + 15

we are told that 7x - 15 = x + 15
6x =30
x = 5

total cakes = x + 7x = 8x = 40