What number added to 15 gives 3 less than 2/7 of 77

please add explanation! ;)

Astick 2 m long is placed vertically at point b. the top of the stick is in line with the top of a tree as seen from point a, which is 3 m from the stick and 30 m from the tree. how tall is the tree?

Choose the more precise measurement. 26.4 cm or 8.39 cm

Find the value of x. round the length to the nearest tenth