Please help me answer problems $3$ and $4.$ I do not understand this. Problem $3.$ For the two torsion members given below, determine the reacting torsion at A and draw the torsion, $\frac{T}{J}G$ and rotation diagrams. Note the changing $J$ values along the member lengths. Shear modulus $G$ is constant.

Problem $4.$ Draw the rotation diagram for the torsion member below. The circular solid section radius changes from $2\mathrm{.}5$ in$.$ to $5$ in$.$ from $B$ to $C,$ and the reverse from $C$ to $D.$ Determine maximum shear stresses along the member length at $A,B,C,D$ and $E.$