The mass is 256.7 because you round it up from 7.
<span>f(x) = ax2+bx+c, is quadratic equation
</span><span>function opening downward if the a<0,
</span><span>kf(x) = -x², a= -1<0
so the answer is </span><span>B.kf(x) </span><span>
</span>
Think of the SS numbers as being a collection of digits. If any of the digits (say the first one for example) are 8 then all the remaining digits can be anything but 8, meaning there are 9 choices for each remaining digit. This effectively becomes an 8 digit number with the constraint that there can only be 9 choices for a digit. This means for the first digit being 8 we have 9⁸ remaining possible numbers. Since we will do this for each of the remaining digits (they each get to be 8 then we count their 9⁸ configurations) we end up with 9(9⁸) or 9⁹≈3.8742E8
A + 4(a - 5) = 5
a + 4a - 20 = 5
5a = 5 + 20
5a = 25
a = 25/5
a = 5 <====
