how do I solve this ? please help I have a test tomorrow and I don’t understand any of this

Answer:
A. 12 is the answer
Step-by-step explanation:
Since DM = 35
it means r+3 and 4r-28 must add together to become 35
So we can put this in an equation:
r+3+4r-28=35
Add 4r and r which is 5r
3-28 is -25
So the equation now looks like this:
5r-25=35
Add 25 on both sides:
5r=60
Divide 5 on both sides:
r=12
Hope this helps!