Chad and Eric left a 20% tip after having lunch at a restaurant. Chad's lunch cost $10. Which equation can you use to find x, the cost of Eric's lunch?
A) 0.2(x + 10) = 5

B) 0.2x = 10 + 5

C) 0.2x + 5 = 10

D) 0.2x + 10 = 5