consider the utility function U = 5x +3y², which has MUx = 5 and MUy = 6y. The indifference curves for this utility function:

a) will have a diminishing marginal rate of substitution of x for y as x increases.

b) will have a constant marginal rate of substitution of x for y as x increases.

c) will have an increasing marginal rate of substitution of x for y as x increases.

d) will be straight lines.

The answer is B, but I don't understand. Please explain