Which statement correctly distinguishes $R$, $\overrightarrow{R}$, and $\hat{R}$ in Coulomb's law?

Which expression is the correct vector form of Coulomb's law after substituting $\hat{R}=\frac{\overrightarrow{R}}{R}$ into $\overrightarrow{F}=\frac{kq1q2}{R^2}\cdot \hat{R}$?

A displacement vector between two charges is $\overrightarrow{R}=3\hat{i}-4\hat{j}$ meters. What is the value of $R^3$ used in the vector Coulomb formula?

Two point charges are $q1=2.0$ microcoulombs and $q2=3.0$ microcoulombs. For the force on $q2$, the displacement vector is $\overrightarrow{R}=0.30\hat{i}+0.40\hat{j}$ meters. Using $k=8.99\times {10}^9$ ${\text{Nm}}^2{\text{/C}}^2$, what is the force vector?

A uniformly charged disk of radius $a$ lies in the $xy$-plane with surface charge density $\sigma$. A test charge $q$ is on the $z$-axis at height $z$. Which setup is the most appropriate first step for an integral solution using concentric rings?