Intro to Proofs (Algebraic, Segment, Angle)

Which property, definition, postulate, or theorem justifies the following statement?
If  $3x-17=26$  , then  $3x=33$  . 

Which property, definition, postulate, or theorem justifies the following statement?

 $\overline{MN}\cong\overline{MN}$  

Which property, definition, postulate, or theorem justifies the following statement?

If K is between J and L, then  $JK\ +\ KL\ =JL$  .

Which property, definition, postulate, or theorem justifies the following statement?

If  $CD+EF=HI$  and  $EF=MN$  , then  $CD+MN=HI$  .

Which property, definition, postulate, or theorem justifies the following statement?

If  $\angle RST\cong\angle LMN$  , then  $\angle LMN\cong\angle RST$  .

Which property, definition, postulate, or theorem justifies the following statement?

If  $\overline{FG}\cong\overline{GH}$  , then  $FG=GH$  .

Which property, definition, postulate, or theorem justifies the following statement?

 $3\left(5a-1\right)=15a-3$  

Which property, definition, postulate, or theorem justifies the following statement?

If  $\angle A$  and  $\angle B$  form a linear pair, then  $\angle A$  and  $\angle B$  are supplementary.

Which property, definition, postulate, or theorem justifies the following statement?

If  $MP=PN$  and M, N, and P are collinear, then P is the midpoint of  $\overline{MN}$  .

Which property, definition, postulate, or theorem justifies the following statement?

If  $\angle R$  is supplementary to  $\angle S$  and  $\angle R$  is supplementary to  $\angle T$  , then  $\angle S\cong\angle T$  .