You would need to multiply the quantity of shrubs bought by the price of each one, so 4p and add that to the price of the soil to get the total cost
The equation becomes 4p + 17.50 = 53.50
Now solve for p:
4p +17.50 = 53.50
Subtract 17.50 from both sides:
4p = 36
Divide both sides by 4:
p = 36/4
p = 9
The answer would be: 4p + $17.50 = $53.50; p = $9.00