Freshman:Sophmore = 5:4

Sophmore:Juniors = 7:8
Juniors:Seniors = 9:7
The total is 2158, what is the amount of each grade?

So far, I got 35:32:224/9 for Freshman:Sophmore:Seniors

I don't know if I'm correct, or what I'm doing. Can you please give me help and explain? thanks so much

LCM(4,7,8,9) = 504

5:4 = 630:504
7:8 = 504:576
9:7 = 576:448

So, we have the class ratios in the sequence

630:504:576:448

Add those up and you have 2158