First you divide everything by 4 which will become b^2+2b-3=0
Then you can factor this which is
(b-1)(b+3)=0
B=1
B=-3 ... I think that's how you do it
Here, Your Original expression is 60x - 24.
Take 12 as common, which is GCD of 24 & 60,
Therefore, It would be:
60x - 24
= 12 * 5x - 12 * 2
= 12 (5x - 2)
In short, your Answer would be 12(5x - 2)
Hope this helps!
Photon
Correct Ans:Option A. 0.0100
Solution:We are to find the probability that the class average for 10 selected classes is greater than 90. This involves the utilization of standard normal distribution.
First step will be to convert the given score into z score for given mean, standard deviation and sample size and then use that z score to find the said probability. So converting the value to z score:

So, 90 converted to z score for given data is 2.326. Now using the z-table we are to find the probability of z score to be greater than 2.326. The probability comes out to be 0.01.
Therefore, there is a 0.01 probability of the class average to be greater than 90 for the 10 classes.