To interpret the regression slope b, use equation (11-18) to answer the following questions.
(a) About how much is the yield increased for every pound of fertilizer applied?
(b) If wheat were worth S2 per bushel and fertilizer cost S.25 per pound, would it be economical to apply fertilizer?
(c) To what price approximately would fertilizer have to drop to make it economical? [The answer to (a) is simply the slope b. Economists refer to b as the "marginal" effect of fertilizer x on yield Y.]