The base of a certain solid is an equilateral triangle with altitude 7. Cross-sections perpendicular to the altitude are semicircles. Find the volume of the solid, using the formula $$V=\int_a^b A(x)\,dx$$ applied to the picture shown above (click for a better view), with the left vertex of the triangle at the origin and the given altitude along the $x$-axis.
Note: You can get full credit for this problem by just entering the final answer (to the last question) correctly. The initial questions are meant as hints towards the final answer and also allow you the opportunity to get partial credit.
The lower limit of integration is $a$ =
The upper limit of integration is $b$ =
The diameter $2r$ of the semicircular cross-section is the following function of $x$:
$A(x)$=
Thus the volume of the solid is $V$ =