A dragster's position as a function of time is given by \(x(t)=b t^{3 / 2}\), where \(b=30.2 \mathrm{~m} / \mathrm{s}^{3 / 2}\). Calculate the \(x\) component of its velocity at \(1.0 \mathrm{~s}\) and at \(4.0 \mathrm{~s}\).