Quick Solution to multiple creepy equations for DS?

[clawhammer]

Can anyone please suggest me any quick way to figure answer to a DS question like this:

A total of $60,000 was invested for one year. Part of this amount earned simple annual interest at the rate of x percent per year, and the rest earned simple annual interest at the rate of y percent per year. If the total interest earned by the $60,000 for that year was $4,080, what is the value of x ?

(A) x = 3y/4

(B) The ratio of the amount that earned interest at the rate of x percent per year to the amount that earned interest at the rate of y percent per year was 3 to 2.

[clock60]

am not sure that i know any efficient way to solve this task , but my little try
here a-part of 60000 that will be invest with x%, the first equation
a*x+(60000-a)*y=4080*100 our initial equation ( *100 here to because x%=x/100 as well as y%)
we need to know what is x-?
for sure we have three unknowns, x,y,a
(1) x=(3/4) insuff as no info about a, but it will be the second equation
second st is interesting
(2) (a*x)/((60000-a)*y)=3/2, let us simplify a little
(2/3)*a*x=(60000-a)*y
now insert this in initial
a*x+(2/3)*a*x=4080*100
a*x=(4080*100*3)/5
and from here we can show say a in terms of x
a=244800/x
but still we have one more unknow y and no info about it
2 insuff
both are suff we have a interms of x, and from 1 st y =4/3 x. so we can solve and find x
resulting equation is too large if you are interested in exact answer i got x=6.12%
my answeer C

[vijchid]

We have
a*x+(60000-a)*y=4080*100

First Statement
X=3/4Y
Insufficient

Second Statement
a/(60000-a)=3/2--
we can find a=36000
the equation now is 36000 x + 24000y=408000
Still insufficient.

Combining both statements we can solve for x.

S0 C.