Opal and Oliver collect stickers and buttons. Oliver has 35 less stickers than buttons. Oliver has 4 times the number of stickers Opal has, and Opal has 40% more buttons than Oliver. After Opal gives Oliver all of her stickers and Oliver gives Opal 60% of his buttons, Oliver has 20 more stickers than buttons. Find the number of buttons Opal has at first.

Opal		Oliver
Buttons	Stickers	Buttons	Stickers
5.6 u + 49	1 u	4 u + 35	4 u
+ 2.4 u + 21	- 1 u	- 2.4 u - 21	+ 1 u
8 u + 70	0	1.6 u + 14	5 u

100%+ 40% = 140% 

140% x 4 u
= ¹⁴⁰₁₀₀ x 4 u
= 5.6 u

140% x 35
= ¹⁴⁰₁₀₀ x 35
= 49 

60% x 4 u
= ⁶⁰₁₀₀ x 4 u
= 2.4 u  

60% x 35 
= ⁶⁰₁₀₀ x 35
= 21 

If another 20 buttons are given to Oliver, he will have equal number of buttons and stickers in the end.
5 u = 1.6 u + 14 + 20
5 u - 1.6 u = 34
3.4 u = 34

1 u = 34 ÷ 3.4 = 10

Number of buttons that Opal has at first
= 5.6 u + 49
= 5.6 x 10 + 49
= 56 + 49
= 105
 
Answer(s): 105