Can someone me with this question?

How do you determine whether a relationship represented as as graph is linear or nonlinear

Find the solution of each of the following.

The party planning committee has to determine the number of tables needed for an upcoming event. if a square table can fit 8 people and a round table can fit 6 people, the equation 150 = 8x + 6y represents the number of each type of table needed for 150 people.