Estimating a manuscript's length if it's set in a particular typeface is called

a. casting off.

b. letterspacing.

c. typography.

d. leading.

The answer is Letter A. Casting off. Casting off is estimating the manuscript's length by counting the number of words required in the manuscript, in order to estimate how many pages needed upon printing. This is necessary in book printing because this will also affect the amount or costs needed.