A ferry can carry 20 bus or 32 cars. if the ferry is loaded with 15 bus, then how many cars would be in the ferry?

Question

A ferry can carry 20 bus or 32 cars. if the ferry is loaded with 15 bus, then how many cars would be in the ferry ?

Answer 1

Let $S$ be the total "space" or "max weight" the ferry has/can carry.

We know that $20b = S$ and $32c = S$ where $b,c$ are respectively the size/the weight of 1 bus or 1 car.

We now want to solve $15b + xc = S$ for $x$ the number of cars. $$ 15b + xc = S = 32c \\ x = 32-15\frac{b}{c} $$ Also $\frac{20b}{32c} = S/S = 1 \implies b/c = 32/20$.

I let you put the result together.