Answer:
Step-by-step explanation:
1) 8a - 19 = 5 +3a
8a - 3a -19 = 5
8a - 3a = 5 + 19
5a = 24
a = 24/5
a = 4.8
2) 8 + 4d - 7 = 4 - d
8 - 7 + 4d = 4 - d
1 + 4d = 4 -d
4d + d = 4 - 1
5d = 3
d = 3/5
d = 0.6
3) 12t + (1-7t) = 31
12t + 1 - 7t = 31
12t - 7t = 31 - 1
5t = 30
t = 30/5
t = 6