Solve this equation

c

//3=6 1/7

c/7 = 6 1/7 ⇒ c = 43 ⇒ 43/7 = 6 1/7

Convert mixed fraction into a simple fraction

6 1/7 ⇒ (6 * 7 + 1) / 7 = 43/7

c/7 = 43/7

proportionality:

a/b = c/d where cross products are equal : ad = bc

a = c

b = 7

c = 43

d = 7

ad = bc ⇒ c7 = 7*43 ⇒ c7 = 301 ⇒ 7c/7 = 301/7 ⇒ c = 43