What is the slope of the line 5x - 3y = 21?

Solve for $y$ to read the slope. From $5x - 3y = 21$, subtract $5x$: $-3y = -5x + 21$. Divide by $-3$: $y = \frac{5}{3}x - 7$. The slope is $\frac{5}{3}$, choice B. Using the shortcut for $Ax + By = C$, the slope is $-\frac{A}{B} = -\frac{5}{-3} = \frac{5}{3}$. Choice A ($-\frac{5}{3}$) forgets that dividing by $-3$ changes the sign of every term. Choice C ($\frac{3}{5}$) inverts the ratio. Choice D (21) is the constant on the right side of the equation, not related to the slope.