The profit function for a set of two electronics products can be expressed by the following expression: where = the number of product 1 units produced and = the number of product 2 units produced. At least 10 units of X1 must be produced and at least 20 units of X2 must be produced. No more than 50 units total can be produced.

Based on the problem description, how is the constraint expressed that no more than 50 units can be produced?

a. X1+ X2 50

b. X1+ X2 50

c. X1^2+ X2^2 50

d. X1^2 + X2^2 50

e. X1 + X2 + X1X2 50