First, use distributive property:
5(2r+6)-12r <em>The original expression; multiply 5 by 2r, and 5 by 6.</em>
10r+30-12r <em>Keep the -12r, just add it on to the end of the number(s) you found</em>
Next, use communitive property:
10r+30-12r <em>What we found in the previous step</em>
-2r+30 <em>Combine the like terms; 10r-12r=-2r, then place the 30 at the end</em>
Done! Your answer is -2r+30.
Hope that helps!