80% of Olivia's amount was $3128 more than David's amount. When Olivia spent 65% of her amount and David spent 35% of his amount, they had the same amount of amount left. Find the amount that David had at first.

	80% of Olivia's amount	Olivia's amount	David's amount
Before	208 u	260 u	140 u
Change		- 169 u (- 65%)	- 49 u (- 35%)
After		91 u	91 u

Percentage of Olivia's amount left
= 100% - 65%
= 35%

Percentage of David's amount left
= 100% - 35%
= 65%

35% = ³⁵₁₀₀ = ⁷₂₀
65% = ⁶⁵₁₀₀ = ¹³₂₀

The amounts of amount that Olivia and David had left were the same.
Make the numerators the same.

⁷₂₀ of Olivia's amount = ¹³₂₀ of David's amount
⁹¹₂₆₀ of Olivia's amount = ⁹¹₁₄₀ of David's amount

Amount that Olivia had = 260 u

80% of the amount that Olivia had
= 260 u x 80%
= 260 u x ⁸⁰₁₀₀
= 208 u

Difference between 80% of Olivia's amount and David's amount
= 208 u - 140 u 
= 68 u

68 u = 3128
1 u = 3128 ÷ 68 = 46

Amount that David had at first
= 140 u
= 140 x 46
= $6440

Answer(s): $6440