Adding 42 to a given positive number gives the same result as squaring the number. Find the number

A. 14
B. 13
C. 7
D. 6

Correct Answer: Option C

C. 7

Explanation

Let the given positive number be x

Then 4 + x = x²

0 = x² – x – 4²

or x² – x – 4² = 0

x² – 7x + 6x – 4² = 0

x(x – 7) + 6(x – 7) = 0

= (x + 6)(x – 7) = 0

x = -6 or x = 7

Hence, x = 7