To cancel a term, it is necessary to add the <em>opposite of the term</em> to both sides of the equation
Step-by-step explanation:
Adding opposites creates a sum of zero. Zero added to anything else does not change the its value. So, adding the opposite of a term effectively removes it from (that side of) the equation.
Perimeter is the area around the shape, so if you look at the space between K and J, the units there are 7. Multiply 7 by 2 (since there are two sides), and then add 2. 2 + 14 = 16.