Since you are given the points of the line then you'll have the slope as:
[tex]m = \frac{x_2 - x_1}{y_2-y_1} [/tex]
substituting the points (0,5) and (-5,0)
[tex]m = \frac{5-0}{0-(-5)} [/tex][tex]m = 1[/tex]
substituting the slope and the point(-3,5) you'll have
[tex]m = \frac{x_2 - x_1}{y_2-y_1} [/tex]
[tex]1 = \frac{x - (-3)}{y - 5}[/tex]
[tex]y - 5 = x + 3[/tex]
[tex]y - x = 3 + 5[/tex]
[tex]y - x = 8[/tex]
or in slope-intercept form
[tex]y = x + 8[/tex]
