Answer:
a=0.8
Explanation:
First I distributed 2.5 into (a+4) and got (2.5a+10)+0.5a=12.4. I then combined like terms which are 2.5a and 0.5a and got 3a+10=12.4. I subtracted 10 from both sides to get rid of it and got 3a=2.4. Later, I divided 3 from both sides to get a which comes out to be 0.8.
Hope this helps you :)