The amount he invested in Fund A was twice as much as the amount he invested in Fund B.
LEt x be the amount invested in Fund B
The amount invested in Fund A is 2x
Fund A returned a 8% profit
Profit amount for fund A is 2x * 8% = 2x * 0.08= 0.16x
Fund B returned a 2% profit
Profit amount for fund B is x * 2% = x * 0.02= 0.02x
total profit from the two funds together was S1800
Profit fund A + profit fund B = 1800
0.16x + 0.02x = 1800
0.18x = 1800
Divide by 0.18 from both sides
x = 10000
he invest $10,000 in Fund B