The answer is three. i think you know where three is located in a number line
125/21 = 150/x
cross multiply
125x = 3150
x = 3150/125
x = 25.2 lbs....rounded up = 26 lbs <==
1. x^2 + 13x + 36 = 0
using powerful & time-sparing quadratic formula :
delta = 13^2 - 4*1*36 = 25 = 5^2
x1 and x2 = (-13 -/+ 5)/2 = -9 and -4
x^2 + 13x + 36 = (x+9)(x+4)
2. other way : complete the square
b^2 + 12b + 32 = b^2 + 2*6b + 6^2 - 6^2 + 32
b^2 + 12b + 32 = (b+6)^2 - 4
b^2 + 12b + 32 = (b+6-2)(b+6+2) = (b+4)(b+8)
3. other way : -4 "ovious" solution : (-4)^2 - (-4) -20 = 0
so the other is : -4 . a2 = -20/1 ---> a2 = 5
a^2 - a - 20 = (a-5)(a+4)
