Question is using standard formula ax+by=c to find the slope by converting into slope intercept form y=mx+b
so we also need to convert ax+by=c into y=mx+b as shown below:



divide both sides by

Now compare it with y=mx+b, we get

So using values of a and b, we can find the slope
compare given equation -5x+2y=15 with ax+by=c, we get:
a=-5, b=2
Now plug both into above formula



Now matching these details with given choices we find that THIRD choice is the final answer.