Let's translate the words into expressions:
11 less than 7 times a number is 
5 more than 6 times the number is 
So we have the equation

Subtract 6x from both sides:

Add 11 to both sides:

The measurement of the second angle is 42°. All of the angles of a triangle add up to a total of 180°. If two angles add up to 138°. Then the last angle has to be 42° (180-138).
I think it's the distributive property. I'm not sure. But I hope this helps.
Answer:
its actaully c because its left alone once you subtract