Ok, this is an economics maths question, I'll try my best to explain

U = (x1)^3/4(x2)^3/4

Find the Marginal Rate of Substitution, (basically dx2/dx1), in terms of x1 and x2. (If it makes it easier just x1 and x2 to p and q or whatever else. I have an answer for this part, this is just more of a check to see if it's right.

And also, what does this simplify to:

-3/4(p^-1/4)(q^3/4)
3/4(p^3/4)(q^-1/4)

Thanks.