Question 1064176
You haven't shown a picture of what the triangle looks like. So it's impossible to determine where points H and D are located (in relation to T, U, V). 


However, I have a feeling that H and D are midpoints of TV and UV (the order isn't clear). If so, then HD is parallel to TU and HD is half of TU


Since HD is half of TU, we know...
HD = half of TU
HD = (1/2)*TU
80 = (1/2)*TU


Isolate TU by multiplying both sides by 2


80 = (1/2)*TU
2*80 = 2*(1/2)*TU
160 = (2/2)*TU
160 = 1*TU
160 = TU
TU = 160