Answer:

Step-by-step explanation:
As we know that:
Sum of the measure of all interior angles of a triangle is always 180°.

Answer:
length of the rectangle=27"
Step-by-step explanation:
length be = l; width be = b
2b-15= l
perimeter= 2(l+b)
=2(2b-15+b)=96
=2(3b-15) =96
3b-15 .=48
3b=48+15=63
b=21. Therefore l = (2 x 21) - 15=42-15 =27"
we have the numbers

we know that
The sum of a number and its additive inverse is 0
so

therefore
the number n is equal to 
the sum is equal to zero
the answer Part a) and Part b) in the attached figure