There were 16 boys
-5:4, 10:8, 15:12, 20:16
-20:16 is 20+16=36
-20 were girls and 16 were boys
It looks like you want to find the short leg (x) of a right triangle with long leg 15 and hypotenuse 18. The Pythagorean theorem gives the relationship between the sides of a right triangle.
18² = 15² + x²
324 = 225 + x²
x² = 324 - 225 = 99
x = √99 ≈ 9.9
The appropriate choice is ...
b) 9.9
To find the range we need to find the vertex of the parabola which is at (-b/2a , y)
-b/2a would be 2/2 = 1 ... so find the y value at x = 1
12 - 2(1) - 15 = 1-17 = -16
So the vertex is at (1,-16)
Since the parabola opens upward from that point the minimum value of the range is y = -16
The range would include the point -16 so it is actually
R = [-16,infinity)
