Answer:
The number is 17 or (-3)
Explanation:
Let the number be x
Subtracts 7,
x - 7
squares the result, and gets 100
(x - 7)² = 100
x² - 14x + 49 = 100
x² - 14x - 51 = 0
x² + 3x - 17x - 51 = 0
x(x + 3) - 17(x + 3) = 0
(x - 17) (x + 3) = 0
x = 17 or (-3)
Here,
We assumed Hiroshi's number would be x,
So,
17 - 7 = (10)² = 100
(-3) - 7 = (-10)² = 100
Thus, Hiroshi's number is 17 or (-3)