3/4 of Chelsia's money = 5/6 of Brian's money
15/20 of Chelsia's money = 15/18 of Brian's money
20 - 18 = 2, so 2 units is $24.
Since 2 units is $24, 1 unit is 24 / 2 = $12
20 + 18 = 38, so in total there is 38 units of money.
1 unit is $12, so 38 units is 38 * 12 = $456.
Hence, Chelsia and Brian have $456 in total.