Answer
b) is correct.
Work Step by Step
We have $$\omega=\frac{v_T}{r}$$
The first child, whose distance from the axis is $r_1=1.4m$, has $v_{T1}=2.2m/s$. The second child is located $r_2=2.1m$ from the axis.
Because $\omega$ is constant, we have $$\frac{v_{T1}}{r_1}=\frac{v_{T2}}{r_2}$$ $$v_{T2}=\frac{v_{T1}\times r_2}{r_1}=3.3m/s$$
