It is the last number minus 3
The answer is 3
I hope I helped
Complete Question
Question 18 (3 points) Solve the problem. (3 points) A solar reflector is made using 31 identical triangular-shaped mirrors, each having sides 2.4m, 2. 3m, 1.5 m. What is the total surface area of the reflector?
A) 33 m2
B) 86 m2
C) 52 m2
D) 34 m2
Answer:
The value is 
Explanation:
From the question we are told that
The sides are a = 2.4 m
b = 2.3 m
c = 1.5 m
Generally the semi perimeter is mathematically represented as

=> 
=> 
Generally the using Heron's formula we have that the surface are a is mathematically represented as

=> 
=> 
Answer: A, C and D
Explanation:
Interference occurs when two waves superimpose to form a wave having a smaller or larger amplitude.
Constructive interference is said to occur when two waves superimpose to produce a wave having larger amplitude. It occurs for the waves having phase difference of multiple of 2π. On the other hand, destructive interference occurs for the waves having phase difference π, 3π, ..and so on.
In the given picture, the bright regions represent constructive interference where as the dark ones between them represent destructive interference. Thus, the correct letters representing constructive interference are: A, C and D.