To solve linear equations, you just need to get the term you don’t know, IMO this case a, on the same side. We can do this by subtracting 5a from both sides:
5a + 14 = -5 + 8a
- 5a
14 = -5 + 3a
Then we just need to solve for a:
14 = -5 + 3a
+ 5
19 = 3a
÷ 3
a = 19/3 = 6 1/3
I hope this helps!