Please help me with this question

Part (a) 3. Jeff Bezos' has 40 hours a week to allocate. His utility function is given by U = C _ 40-D: 2 where C is consumption and / is leisure. He therefore has a marginal utility of leisure of 40 - I and a marginal utility of consumption of 1. Jeff's wage is $36 billion per year so, in units of billions, Jeff faces the following budget constraint: C = (1 -t) x 36 x (40 - 1). a. [5 points] Jeff's choice of labor, z = 40-I, depends on the tax rate. Find an expression for Jeff's optimal choice of z. The expression will depend on t. b. The income and substitution effects of higher taxes on Mr. Bezos's labor supply go in opposite directions. Is the income effect positive or negative here? Is the substitution effect positive or negative here?. c. What tax rate t of the options below would maximize the revenue made from Jeff Bezos, given this labor supply? If you don't think you did the parts above right then briefly explain the economics of what is going on here