First thing, you need to transform this equation to the form of y = ax + b
So you get:
2x + 5y = 8
5y = -2x + 8

In the form of y = ax + b, a is the slope.
In

, you can see "

", and always the number before x is the slope
So, the slope of 2x + 5y = 8 is

Hope this Helps :)