I would help you but it me hard for me too
Beverley is right
explanation
there is 3 answers
0,9,3
hope this helps
cauculator link: https://www.symbolab.com/solver/functions-calculator
:D
from Kenny
all the best!
Let 
be the random variable for the number of marks a given student receives on the exam.
10% of students obtain more than 75 marks, so
where 
follows a standard normal distribution. The critical value for an upper-tail probability of 10% is
where 
denotes the CDF of , and 
denotes the inverse CDF. We have
Similarly, because 20% of students obtain less than 40 marks, we have
so that
Then 
are such that
and we find
