Dana and Sean collect beads and erasers. Sean has 60 more erasers than beads. Sean has 4 times the number of beads Dana has, and Dana has 30% more erasers than Sean. After Dana gives Sean all of her beads and Sean gives Dana 70% of his erasers, Sean has 39 more beads than erasers. Find the number of erasers Dana has at first.

Dana		Sean
Erasers	Beads	Erasers	Beads
5.2 u + 78	1 u	4 u + 60	4 u
+ 2.8 u + 42	- 1 u	- 2.8 u - 42	+ 1 u
8 u + 120	0	1.2 u + 18	5 u

100% + 30% = 130% 

130% x 4 u
= ¹³⁰₁₀₀ x 4 u
= 5.2 u

130% x 60
= ¹³⁰₁₀₀ x 60
= 78 

70% x 4 u
= ⁷⁰₁₀₀ x 4 u
= 2.8 u  

70% x 60 
= ⁷⁰₁₀₀ x 60
= 42 

If another 39 erasers are given to Sean, he will have equal number of erasers and beads in the end.
5 u = 1.2 u + 18 + 39
5 u - 1.2 u = 57
3.8 u = 57

1 u = 57 ÷ 3.8 = 15

Number of erasers that Dana has at first
= 5.2 u + 78
= 5.2 x 15 + 78
= 78 + 78
= 156
 
Answer(s): 156