Answer
$c = 11$ cm
Work Step by Step
$c^{2} = a^{2} + b^{2} - 2abcos(C)$
$c^{2} = (10)^{2} + (12)^{2} - 2(10)(12)cos(60)$
$c^{2} = 100 + 144 - 240cos(60)$
$c^{2} = 244 - 120$
$c^{2} = 124$
$c = ±\sqrt {124}$
$c = ±11.1355...$
$c = 11.1355...$ (The length $c$ cannot be negative)
$c = 11$ cm
