Simple interest is given by:

$SI=\frac{PRT}{100}$

Here, rate is same and interest is also same.

So, principal is inversely proportional to time.

Times are:

$2$ years, $3$ years and $4$ years.

Therefore, ratio of amounts invested is:

$\frac{1}{2}:\frac{1}{3}:\frac{1}{4}$

LCM of $2,3,4$ is $12$.

Multiplying each term by $12$:

$6:4:3$