$$ \begin{cases} R&=\frac{75.0}{2}\ut{cm}=\frac{3}{8}\ut{m}\\v_0&=105\ut{km/h}=\frac{175}{6}\ut{m/s}\\\Delta \theta &= 30\ut{rev}=60\pi\ut{rad}\\v_1&=0\\\end{cases} $$$$\ab{a}$$$$ \begin{aligned}\omega&=\frac{v}{R}\\&=\frac{700}{9}\ut{rad/s}\\&\approx 77.77777777777777\ut{rad/s}\\&\approx 77.8\ut{rad/s}\\\end{aligned} $$$$\ab{b}$$$$2\alpha \Delta \theta=\omega^2-{\omega_0}^2,$$$$ \begin{aligned}..