Ok, the first thing to note is that the ground and the two parts of the tree form a right triangle (see image).

Sideais the (still standing) lower part of the tree, sidecis the (broken off) upper part of the tree, and sidebis the ground.

Since we know that the total height of the tree was 60 ft, we can write:

ft

We now have two unknown variables, but only equation. So we need one more equation. Luckily for a right triangle we have equations that relate angles and side lenghts. The sine of an angle in the triangle equals the opposing side divided by the hypotenuse side:

By combining the two equations you can now findaandc.

Afterwards you use Pythagoras' theorem to find the one remaining unknown sideb: