A consumer's utility function is U(x₁,x₂,x₃,x₄)=3x₁+x₂x₃+x₄x₅-x₁x₅. How does the number of units of good 1 that the consumer is willing to give up in order to obtain an additional unit of good 3 change if only his consumption x₅of good 5 changes?

a.

It goes up if x₅goes up.

b.

It stays the same.

c.

None of the other answers.

d.

It goes down if x₅goes up.