Answer:
None of these answers would work. You may have typed some wrong perhaps?
Answer:
First blank: 5
Last blank: 20
Step-by-step explanation:
Going by the hint that is shown:

c = 1
r = 5
and

c = 4
r = 20
Hope this helps!
Answer:
A, C
Step-by-step explanation:
Only B is containing a variable .
Answer:
x=3m-n
Step-by-step explanation:
Isolate x.
3m=n+x
3m-n=x
x=3m-n