Question

You buy the same number of brushes, rollers and paint cans. Write an expression in simples form that represents the total amount of money you spend for painting supplies. Paint $21.79
Brush $3.99 and Paint Roller $6.89

Answer 1

T= 21.79x + 3.99x + 6.89x where t is the total cost and x is the number of brushes/rollers/paint cans you buy. You don't need a different variable for each item because you buy the same amount of each.

Answer 2

If you purchase of each item, then you'll pay  3.99N  for brushes,
21.79N  for cans of paint, and  6.89N  for rollers. 
                      3.99N + 21.79N + 6.89N

                 =  N (3.99 + 21.79 + 6.89)

                 =        32.67 N .