You are quoting from page 49 from William Strunk and E. B. White’s famous book on writing, Elements of Style. Assuming you do not use the author’s names in a phrase leading into the quote (an attribution) write the exact parenthetical citation below:

The slope of a linear equation is equal to the change in the value of the dependent variable divided by the change in the value of the independent variable. in this problem, the dependent variable is the profit while the independent variable is the worker's average pay. if the profit is said to increase by 1500 when worker's average pay decrease by 450, the slope is equal to 1500/(-450)=-3.33

The number of syllables is 6