Answer
It must sail 156 km.
Work Step by Step
When the boat is blown by the wind, a triangle is created between the original starting position, the new starting position to the east, and the target destination. The two sides of the triangle are 100km and 120km. Pythagorean's Theorem must be used to find the final side. The missing side is distance that the boat must sail to reach its destination.---$100^{2}$+$120^{2}$=24400
$\sqrt24400$=156km
