Shannon and Owen collect erasers and marbles. Owen has 90 less erasers than marbles. Owen has 4 times the number of erasers Shannon has, and Shannon has 40% more marbles than Owen. After Shannon gives Owen all of her erasers and Owen gives Shannon 60% of his marbles, Owen has 15 more erasers than marbles. Find the number of marbles Shannon has at first.

Shannon		Owen
Marbles	Erasers	Marbles	Erasers
5.6 u + 126	1 u	4 u + 90	4 u
+ 2.4 u + 54	- 1 u	- 2.4 u - 54	+ 1 u
8 u + 180	0	1.6 u + 36	5 u

100%+ 40% = 140% 

140% x 4 u
= ¹⁴⁰₁₀₀ x 4 u
= 5.6 u

140% x 90
= ¹⁴⁰₁₀₀ x 90
= 126 

60% x 4 u
= ⁶⁰₁₀₀ x 4 u
= 2.4 u  

60% x 90 
= ⁶⁰₁₀₀ x 90
= 54 

If another 15 marbles are given to Owen, he will have equal number of marbles and erasers in the end.
5 u = 1.6 u + 36 + 15
5 u - 1.6 u = 51
3.4 u = 51

1 u = 51 ÷ 3.4 = 15

Number of marbles that Shannon has at first
= 5.6 u + 126
= 5.6 x 15 + 126
= 84 + 126
= 210
 
Answer(s): 210