How can I Solve 11a-7=8a + 9

you need to isolate the variable on one side and the number on the other

1) subtract 8a from both sides of the equation; 3a - 7 = 9

2) add 7 to both sides of the equation; 3a = 16

3) divide both sides by 3; a=16/3 or a=5.33

Add 7 to - 7 and do the same thing to 9. so your equation should be 11a=8a+16. once you have that you need to find (A) so you subtract 8a from 11a which is 3a. 8a on the other side of the equation should be out of the equation leaving ypu with 3a=16. divide 3 on each side and A equals 5.3.