Compute the length of the curve ${\bf r\it(t)} = 3 t {\bf \, i} + 6 t {\bf \, j} +(t^2+5){\bf \, k}$ over the interval $0 \le t \le 4$.

HINT: use the formula $$\int \sqrt{ t^2 + a^2} \, dt = \frac{1}{2} t \sqrt{t^2+a^2} + \frac{1}{2} a^2 \ln \left( t + \sqrt{t^2+a^2} \right) + C$$

$L=$