See the attached picture. You'll find a tree with four branches at level 1 (each of the four sectors of the spinner). Each of these branches is divided in four sub-branches: the possible results of tossing two coins (HH, HT, TH, TT).
So, there are 16 possible outcomes (numbered below each leaf).
If you want to roll an odd number, you have to take branch 1 or 3 at first level.
Then, for each of those, you have to toss exactly one head, so you have to take HT or TH.
The good outcomes are thus 2, 3, 10 and 11, leading to a probability of 4/16=1/4=25%.
