Hi Aidan M.
With the points (-3,10) and (2, 5)
Let (-3,10) be your first point (x1, y1)
Let (2,5) be your second point (x2, y2)
For a line in Slope Intercept Form
y = mx + b
First use the two points given to find the slope
Second use one of the points to solve for b
Then just plug everything into your line
m = (y2 - y1)/(x2 - x1)
m = (5 - 10)/(2 -(-3)) = -5/5 = -1
Slope m = -1
y = -x + b
Now just solve for b
I will use your first point (-3, 10)
10 = -1(-3) + b
10 = 3 + b
10 - 3 = b
b = 7
y = -x + 7
You can graph this at Desmos.com. Of course there are other way to solve you can also try the Point Slope Form and see if you get y + x = 7 give it a try.