answer is C.
from statement i) we can formulate the equation.
principal 1* .75y + principal 2*y = 4080
so it is insuff...
from statement 2) we know that amount invested in interest rate x is 3600 and in interest rate y is 2400.
now we we know that total interest earned is 4080
but since we have no idea about the interest rate it is insuff...
now if we combine both the statement we get,
3600*.75y + 2400y = 4080
we can easily calculate the rest from here.
so C is the answer.