I'm having trouble solving the interest rate questions. I know the formulas but am not correctly answering the questions in this topic. Please help.

Question:
Robin split a total of $24,000 between 2 investments, X and Y. If investment earns 7% simple annual interest, how much of that total did Robin put into investment Y?
1. Each investment earns the same dollar amount of the interest annually.
2. Investment X earns 5 percent simple annual interest.

Answer is C.

I know for data sufficiency I don't need to do the math. But since this is a weak topic area for me, can you please also explain how to rephrase and how I can set up the math in case I had to solve it as a Problem Solving question? Any insight on this question would be great!

Question:
Robin split a total of $24,000 between 2 investments, X and Y. If investment earns 7% simple annual interest, how much of that total did Robin put into investment Y?
1. Each investment earns the same dollar amount of the interest annually.
2. Investment X earns 5 percent simple annual interest.



P=24k; P= X+Y
Interest= PNR/100;
Interest(X)= (24000-Y)*1*R/100; Interest( Y)= (24000-X)*1*R/100

What is X?

Using BDACE Grid:
2) R(X)= 5%
But we dont know how much is the investment Robin put into X. Hence INSUFF

1) Each investment earns the same $ amount of the interest annually.
Interest(X)= Interest (Y) but we dont know about the Rate of Interest for either X or Y. Hence INSUFF

Using 1 and 2,

we know the Interest Rate for X; Also the $ of Interest Earned Annually from X and Y are equal. There by we can find how much invested in Y.

Thanks

ok:
first, find expressions for the interest on each of the two accounts:
interest on x = 0.07x
interest on y = (rate)(24000 - x)

(1) alone:
0.07x = (rate)(24000 - x)
this is one linear equation, with two unknowns, so it can't be solved uniquely.
insufficient

(2) alone:
interest on x = 0.07x
interest on y = 0.05(24000 - x)
but there's no equation relating these two things
insufficient

together:
0.07x = 0.05(24000 - x)
linear equation in one variable --> can be solved uniquely
sufficient

answer = c