1. 8a-19=5+3a
2. 8+4d-7=4-d
3. 5, 12t+(1-7t)=31

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

no not all of them.

step-by-step explanation:

some of them have a square base.

after simplifying it i got: -36.25 as my answer. hope that !