Question

Please answer this and thank you If DE=4x+10, EF=2-1, and DF=9x-15, find DF.

Answer 1

I hope that 2-1 means 21.

DE + EF = DF
4x + 10 + 21 = 9x - 15
4x + 31 = 9x - 15
31 = 9x - 4x - 15
31 = 5x - 15
46 = 5x
x = 9 1/5 = 9.2

You want 9x - 15
9*9.2 - 15
82.8 - 15
67.8 <<<<< answer. 
If I have given the wrong meaning to 2-1 (which could mean 1) leave another note and I will correct my work.