Lynn and Brandon collect coins and erasers. Brandon has 40 less coins than erasers. Brandon has 2 times the number of coins Lynn has, and Lynn has 20% more erasers than Brandon. After Lynn gives Brandon all of her coins and Brandon gives Lynn 75% of his erasers, Brandon has 15 more coins than erasers. Find the number of erasers Lynn has at first.

Lynn		Brandon
Erasers	Coins	Erasers	Coins
2.4 u + 48	1 u	2 u + 40	2 u
+ 1.5 u + 30	- 1 u	- 1.5 u - 30	+ 1 u
3.9 u + 78	0	0.5 u + 10	3 u

100%+ 20% = 120% 

120% x 2 u
= ¹²⁰₁₀₀ x 2 u
= 2.4 u

120% x 40
= ¹²⁰₁₀₀ x 40
= 48 

75% x 2 u
= ⁷⁵₁₀₀ x 2 u
= 1.5 u  

75% x 40 
= ⁷⁵₁₀₀ x 40
= 30 

If another 15 erasers are given to Brandon, he will have equal number of erasers and coins in the end.
3 u = 0.5 u + 10 + 15
3 u - 0.5 u = 25
2.5 u = 25

1 u = 25 ÷ 2.5 = 10

Number of erasers that Lynn has at first
= 2.4 u + 48
= 2.4 x 10 + 48
= 24 + 48
= 72
 
Answer(s): 72