Answer:
a = 3.75
Explanation:
First distribute the -3 to (a - 6), which gives you the equation, 19a - 3a + 18 = 78. Then subtract the 3a from 19a, which gives you 16a + 18 = 78. Then subtract 18 from both sides and you get 16a = 60. Divide 60 by 16 and you get 3.75 as your a.