Please help me with this

Answer:
The answer is s = 1.
Step-by-step explanation:
Opposite sides of a parallelogram are equal so,
3s + 19 = s + 21
3s - s = 21 - 19
2s = 2
s = 1
next,
s + 21 =? 3s + 19
1 + 21 equal to (?) 3(1) + 19
22 = 22
so the answer is correct