Natalie, Usha, Gwen and Shannon jointly contributed to the cost of a present for their colleague. Natalie's contribution is ³₄ of the total contribution made by the four girls. The ratio of Shannon's contribution to the total of Usha's and Gwen's contribution is 5 : 2. What is the total contribution by the four girls if Usha's contribution is ²₃ of Gwen's contribution and the total amount contributed by Natalie and Shannon is $2600?

Natalie	Usha	Gwen	Shannon	Total
3x35	1x35			4x35
	2x5		5x5
	2x2	3x2
105 u	4 u	6 u	25 u	140 u

Working backwards.

Total amount that Usha and Gwen had is the combined repeated identity.
LCM of 2 and 5 = 10

Total amount that Usha, Gwen and Shannon had is the next combined repeated identity.
LCM of 1 and 35 = 35 

Total amount contributed by Natalie and Shannon
= 105 u + 25 u
= 130 u

130 u = 2600

2 u = 2600 ÷ 130 = $20

Total contribution by the four girls
= 140 u
= 140 x 20
= $2800

Answer(s): $2800