Definition of reaction rate

Exercise 1

Butane burns in oxygen: $2\;C_4H_4(g)$ $+$ $13\;O_2(g)$ $\longrightarrow $ $8\;CO_2(g)$ $+$ $10\;H_2O(g)$ If in a given time, butane reacts with a rate of $v_{C_4H_4}$ $=$ $-0.30\frac{mol}{L\cdot s} $ What are the product formation rates?

$v_{CO_2}$ $=$ $1.20 \frac{mol}{L\cdot s}$ $v_{H_2O}$ $=$ $1.50 \frac{mol}{L\cdot s}$