A Manufacturer Will Supply X Units of a Certain Commodity $p = S ( x )$

Multiple Choice

A manufacturer will supply x units of a certain commodity to the market when the price is $p = S ( x )$ dollars per unit,where $S ( x ) = 21 + 2 x - 2.5 \sin \pi x$ . What is the average price per unit as the level of production increases from $x = 4$ to $x = 7 ?$ (Round to the nearest cent.)

A) $32.53 per unit
B) $32.00 per unit
C) $31.47 per unit
D) $42.47 per unit