First of all be more spusific in your question
20:25 now simp that and you will have your answer
Nice... you might have put the wrong picture lol
Since they're vertical angles, they're equal in degree measure
since they're equal, we can make the two expressions equal to each other
5a - 1 = 2a + 20
add 1 to both sides
5a = 2a + 21
subtract 2a from both sides
3a = 21
divide both sides by 3a
a = 7
now, plug the answer you found for a into one of the two expressions
5a - 1 becomes (5*7) - 1, which equals 34
to double check that they're equivalent (since they're vertical angles)
2a + 20 becomes (2*7) + 20, which equals 34
both angles are 34 degrees!