I need help with 8 and 11 show ur work and check it

Answer:
c=15. 11 is x = 35
Step-by-step explanation:
Start by subtracting 10 from 25
25-10 = 15
Check:
10 + 15 = 25
Therefore, the answer is c = 15
20 + 15 is 35
Check with 35 - 15 = 20
Therefore, x = 35 is the answer