#### Answer

$y=-x + 7$

#### Work Step by Step

RECALL:
(i)
The slope-intercept form of a line's equation is $y=mx+b$ where $m$ = slope and $b$ = y-intercept.
(ii) The formula for slope is $m=\dfrac{y_2-y_1}{x_2-x_1}$.
Solve for the slope using the formula above to have:
$m=\dfrac{-1-3}{8-4}=\dfrac{-4}{4}=-1$
Thus, the tentative equation of the line is $y=-x + b$.
Solve for the value of $b$ by substituting the x and y-coordinates of one point into the tentative equation to have:
$y=-x+b
\\3 = -4+b
\\3+4=b
\\7=b$
Therefore, the equation of the line in slope-intercept form is $y=-x + 7$.