Question

3tens+5 tens= _tens=_

Answer 1

Three tens (3) plus five tens (5) would be eight tens (8), which is eighty (80).
I don't know if this is the correct answer nor if this is how you are supposed to answer it, but it's my guess.

Hope this answers your question correctly.

Answer 2

3tens  + 5 tens = 80 tens= 80