Triangle ABC is a right angle triangle. So, the Pythagoras theorem can be applied. We want to determine the value of w. The Pythagoras theorem is expressed as
Hypotenuse^2 = opposite side^2 + adjacent side^2
Looking at triangle ABC,
The hypotenuse which is the longest side of the triangle is 20
The adjacent side of the triangle with angle C as the reference angle is 12. The opposite side of the triangle is w. Therefore,