A man measured the angle of elevation of the top of a tower to be 70deg,When he walked 300meters further, the angle of elevation of the top was 35deg, what is the height of the tower?

rmonterde: Nice homework problem. We're not going to just give you the answer, but will help you out if you show some effort here and get stuck.

As a starter, draw the problem. With the tower on one side (doesn't matter about the height) then draw an imaginary line to indicate the 70° angle to the top of the "tower". Then draw a further line at 35° to the top of the tower. Then fill in what you know. Start with that and see if you can figure it out

Use the law of tangents according to the diagram. Solve for x and y.
y being the height of the tower.

i.e. one equation would be \frac{y}{300+x}=tan(35)