what is an equation for the following table x 5 6 7 8 9
y 5 7 9 11 13

Can you find the gradient of this line?
If so, then use:

\frac{y - y_1}{x - x_1} = m

where m is the slope or gradient of the line,
y1 being one y coordinate and x1 being the corresponding x coordinate.

2x-5=y

Yes, that's it! Well done :)