Question

4r+3=r+21

How do I do this?

Answer 1

You first:
4r+3-3=r+21-3
4r=r+18 
4r-r=r-r+18
3r=18
3r/3=18/3
r=6
remember that what you do in one side, do it in the other

Answer 2

simplify: 4r + 3 = r + 21, then reorder the terms: 3 + 4r = r + 21.
Reorder the terms 3 + 4r = 21 + r. Solve: 3 + 4r = 21 + r. 
Move all terms containing r to the left, all other terms to the right.
Solving for variable 'r'.
 Add '-1r' to each side of the equation. 3 + 4r + -1r = 21 + r + -1r.
 Combine like terms: 4r + -1r = 3r3 + 3r = 21 + r + -1r
 Combine like terms: r + -1r = 0 3 + 3r = 21 + 0 3 + 3r = 21
 Add '-3' to each side of the equation. 3 + -3 + 3r = 21 + -3
 Combine like terms: 3 + -3 = 0 0 + 3r = 21 + -3 3r = 21 + -3
 Combine like terms: 21 + -3 = 18 3r = 18
Divide each side by '3'. r = 6 Simplifying r = 6