−18(2h+4)+12=−74
what is the value of h?

Your goal is to get h by itself -18(2h+4)+12=-74
first distribute 
-36h-72+12=-74
second combine like terms
-36h-60=-74
third get h by itself by adding 60 to the other side
-36h=-14
forth divide -36
h=0.38 
to check your answer you plug in your answer to the equation and you'll get -73.68 but round it to nearest 10th you get -74
 

Understanding what? lol