80% of Gabby's amount was $899 more than Billy's amount. When Gabby spent 65% of her amount and Billy spent 20% of his amount, they had the same amount of amount left. Find the amount that Billy had at first.

	80% of Gabby's amount	Gabby's amount	Billy's amount
Before	64 u	80 u	35 u
Change		- 52 u (- 65%)	- 7 u (- 20%)
After		28 u	28 u

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

Percentage of Billy's amount left
= 100% - 20%
= 80%

35% = ³⁵₁₀₀ = ⁷₂₀
80% = ⁸⁰₁₀₀ = ⁴₅

The amounts of amount that Gabby and Billy had left were the same.
Make the numerators the same.

⁷₂₀ of Gabby's amount = ⁴₅ of Billy's amount
²⁸₈₀ of Gabby's amount = ²⁸₃₅ of Billy's amount

Amount that Gabby had = 80 u

80% of the amount that Gabby had
= 80 u x 80%
= 80 u x ⁸⁰₁₀₀
= 64 u

Difference between 80% of Gabby's amount and Billy's amount
= 64 u - 35 u 
= 29 u

29 u = 899
1 u = 899 ÷ 29 = 31

Amount that Billy had at first
= 35 u
= 35 x 31
= $1085

Answer(s): $1085