For c to be positive, and for b to be negative, m must be negative and n must be negative.
X^2 - bx + c = (x - m)(x - n).
c is the product of m and n. If both m and n are positive, c would be positive. However b is the sum of m and n, therefore to make b negative, both m and n must be negative to ensure that the product of m and n is positive
It is 1.5 times because $63 divided by $42 is $1.5.
I hope this is what you meant.
First, add all the numbers together, which is 68. Then divided 100 by 68, which gives you the number 1.47, and that's your answer.