(a) If the units for $x$ are feet and the units for $a(x)$ are pounds per foot, what are the units for $da/dx\,?$

A. pounds per foot
B. pounds
C. foot
D. pounds per square foot

(b) If the units for $x$ are feet and the units for $a(x)$ are pounds per foot, what units does $\int_{2}^{\,8} {a(x)}\,dx$ have?

A. foot
B. pounds
C. pounds per square foot
D. pounds per foot