Part B
The units of the momentum of the t-shirt are the units of the integral $\int_{t=0}^{t=t_L} F(t) dt$, where $F(t)$ has units of N and $t$ has units of s. Given that 1 N = 1 kg $\cdot$ m/s$^2$, the units of momentum are:
kg $\cdot$ m/s$^2$
kg/s
kg $\cdot$ m/s
kg $\cdot$ m/s$^3$