Need an answer as a Substitution method please !!!

Question

1. Beth and Aliyah are selling cheecakes. People can buy French cheescakes and chocolate cheecakes. Beth sold 7french cakes and 10 chocolate cakes for a total of 316 dollars. Aliyah sold 5 French cheescakes and 5 marble cheescakes for a total of 185 dollars what is the cost of one French cake and one chocolate cake

Answer 1

7F + 10C = 316

5F + 5C = 185 ---> F + C = 37 ---> C = 37 - F

7F + 10(37-F) = 316

7F + 370 - 10F = 316

-3F + 370 = 316

-3F = -54

F=-54/-3 = 18

So

F = 18

C = 19 <--- per equation in bold above