90% of Ivory's amount was $738 more than Japheth's amount. When Ivory spent 60% of her amount and Japheth spent 10% of his amount, they had the same amount of amount left. Find the amount that Japheth had at first.

	90% of Ivory's amount	Ivory's amount	Japheth's amount
Before	40.5 u	45 u	20 u
Change		- 27 u (- 60%)	- 2 u (- 10%)
After		18 u	18 u

Percentage of Ivory's amount left
= 100% - 60%
= 40%

Percentage of Japheth's amount left
= 100% - 10%
= 90%

40% = ⁴⁰₁₀₀ = ²₅
90% = ⁹⁰₁₀₀ = ⁹₁₀

The amounts of amount that Ivory and Japheth had left were the same.
Make the numerators the same.

²₅ of Ivory's amount = ⁹₁₀ of Japheth's amount
¹⁸₄₅ of Ivory's amount = ¹⁸₂₀ of Japheth's amount

Amount that Ivory had = 45 u

90% of the amount that Ivory had
= 45 u x 90%
= 45 u x ⁹⁰₁₀₀
= 40.5 u

Difference between 90% of Ivory's amount and Japheth's amount
= 40.5 u - 20 u 
= 20.5 u

20.5 u = 738
1 u = 738 ÷ 20.5 = 36

Amount that Japheth had at first
= 20 u
= 20 x 36
= $720

Answer(s): $720