$(10$ Percent$)($Text Problem $5\mathrm{.}3)$ Refer to Chapter $5$ of the text Masonry Structures. Find the following for grouted masonry made with a normal$-$weight $8-$inch $($nominal$)$ hollow concrete block having a compressive strength of $3,000$ psi, Type $S$ mortar, and $4,000$ psi grout:

$($a$)$ What strength would be expected using the principle of superposition of strengths? Explain. Compare with code values.

$($b$)$ Why have some researchers found the strengths calculated using superposition to overestimate compressive strength?