For 3 find the total area for the big semicircle, then find the area of the smaller one and subtract it. It would be the same for 4 but instead you find the total area of the square (24 x 24) and then subtract the semicircle are. (you were wrong on #4)
A unit vector in the direction of a would be the vector a multiplied by a factor such that the length of vector a is unity. The magnitude of a is given by: |a| =sqrt(4^2+3^2+2^2) [ I got lazy instead of writing (-4)^2+(-3)^2+2^2] =sqrt(29).
So the univector is a/sqrt(29), or (-4/sqrt(29),-3/sqrt(29), 2/sqrt(29), or simply (-4,-3,2)/sqrt(29).
