Hi,

Im trying to do this question

$\displaystyle y$ is directly proportional to $\displaystyle x$ and $\displaystyle y = 21$ when $\displaystyle x = 7 $. Find the value of $\displaystyle y$ when $\displaystyle x = 13$

$\displaystyle y = \frac{k}{x} = 21$

$\displaystyle = \frac{k}{7}$

$\displaystyle = 21 X 7 $

$\displaystyle = 147 $

Now put 147 into the formulae with $\displaystyle x$

$\displaystyle y = \frac{147}{13}$

$\displaystyle = 0.something $

Answer book says 39, how?

Thanks