Pla me asap for 12 and 13 (show ! ) + lots of points!

For 12. Neil's mistake was that he didn't combine like terms of both the constant and numbers with both the variable of k. 9 and -8 are both constants so you combine it and get an answer of 1 since 9+ -8 is 1. 12k and k both have the variable of k so you combine it and get 13k. 

The simplified version should be: 13k+1=12k-1

For 13. The third expression would be equivalent to the expression above listed as 12r+6s. The third expression is 4(3r+s)+2s and if you do PEMDAS you will get the same answer. Parentheses, 4 times 3r is 12r and 4 times s is 4s and after that you get 12r+4s+2s. As said before, if they have like terms you combine it so you get 12r+6s and it will equal the same as the one shown above.

Hope this helped you and would love brainiest!  

Okay so for every triangle has three angles that always add up to 180 degrees. and to tell the difference between whether they are secure, right or obtuse is that acute: has one angle that is less than 90 degrees. right triangle means there is at least one angle that is exactly 90 degrees. and an obtuse angle has an angle that is bigger than 180 degrees. i’ll do #13 as an example: 13. 40 and 50 so if every triangle has 180 degrees 40+50= 90 degrees then180-90= 90 degrees so the third angle is 90 degrees and because this triangle has a 90 degree angle it means it is a right triangle