Is the graph of a linear equation always horizontal

Danielle earns a 7.25% commission on everything she sells at the electronics store where she works. she also earns a base salary of $750 per week. what were her sales last week if her total earnings for the week were $1,076.25?

If x is 6, then 7x= a. 13 b. 42 c. 42x d. 76

Can you divide 25 into 4 equal groups? explain why or why not.