(c)
They will encounter if
$10 + 6t = 3 + t^{2}\ \ \ \ \Rightarrow \ \ \ t^{2} - 6t - 7 = 0\ \ \ \ \Rightarrow \ \ \ t = 7$
At $t = 7s$, moving in a first point
$v_{1} = \frac{d}{dt}(10 + 6t) = 6$ cm/s
At $t = 7s$, moving in a second point
$v_{2} = \frac{d}{dt}\left( 3 + t^{2} \right)$
$= 2t = 2 \times 7 = 14\ cm/s$
$\therefore$ Resultant velocity $= v_{2} - v_{1} = 14 - 6 = 8$ cm/s