"Line crosses points M and N:

M(2;6), N(-2;-6), find the equation for it"

The only formula I found was $\displaystyle y-y1=\frac{y2-y1}{x2-x1}(x-x1)$

It works, but this is grade 9 (in our country) exercise, I think there should be a simpler way. Is there?