Natalie and Will collect erasers and pens. Will has 80 less erasers than pens. Will has 3 times the number of erasers Natalie has, and Natalie has 40% more pens than Will. After Natalie gives Will all of her erasers and Will gives Natalie 60% of his pens, Will has 24 more erasers than pens. Find the number of pens Natalie has at first.

Natalie		Will
Pens	Erasers	Pens	Erasers
4.2 u + 112	1 u	3 u + 80	3 u
+ 1.8 u + 48	- 1 u	- 1.8 u - 48	+ 1 u
6 u + 160	0	1.2 u + 32	4 u

100%+ 40% = 140% 

140% x 3 u
= ¹⁴⁰₁₀₀ x 3 u
= 4.2 u

140% x 80
= ¹⁴⁰₁₀₀ x 80
= 112 

60% x 3 u
= ⁶⁰₁₀₀ x 3 u
= 1.8 u  

60% x 80 
= ⁶⁰₁₀₀ x 80
= 48 

If another 24 pens are given to Will, he will have equal number of pens and erasers in the end.
4 u = 1.2 u + 32 + 24
4 u - 1.2 u = 56
2.8 u = 56

1 u = 56 ÷ 2.8 = 20

Number of pens that Natalie has at first
= 4.2 u + 112
= 4.2 x 20 + 112
= 84 + 112
= 196
 
Answer(s): 196