1. The problem statement, all variables and given/known data This is a second (university) year calculus problem dealing with calculus of multiple variables. In economics, utility is a measure of the relative satisfaction from, or desirability of, consumption of goods. A utility function u = u(a,b) gives the utility from consuming a units of a particular good and b units of another good. The utility function for Plike Mank's consumption of c units of cheese and m units of marbles is given by u(c,m) = 2(c^2)m. After this explanation there were some questions regarding the practical meaning of the partials, calculate the partials etc. Part (d) Plike's consumption of cheese and marbles is constrained by his salary. Write down a constraint equation if a unit of cheese cost $18, a unit of marbles cost $12 and he spends $216 on cheese and marbles. 2. Relevant equations Don't know 3. The attempt at a solution I'm not even sure what to do. I missed a couple of lectures this semester and I'm completely lost. Even if someone could point me to the relevant chapter in my textbook I'd be happy. I have never come across a constraint equation before.