30 ft. tall. You must find the ratios and compare. 2/20=3/x The best way I know to do this is to cross multiply. 2 times x and 20 times 3. So, 2x= 60. Divide by 2 and you get x =30. The height of the tree would be 30 ft. You could also find the proportion. 20/2= 10, so the height,x, over 3 would be equal to 10. 3 times 10 is equal to 30.