I think this is the problem that you meant because I solved in another site a couple of days ago :

Pablo invested his savings in two investment funds. The amount he invested in Fund A was 4 times as much as the amount he invested in Fund B. Fund A returned a 2% profit and Fund B returned a 4% profit. How much did he invest in Fund A, if the total profit from the two funds together was $1440? 

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Let amt. invested in B = "x".

The amt. invested in A = "4x"

Equation:

interest + interest = interest

0.02(4x) + 0.04(x) = 1440

Multiply thru by 100 to get:

2(4x) + 4(x) = 144000

12x = 144000

x = $12,000 (amt invested in B)

4x = $48,000 (amt. invested in A)