Simplify
4b−7−15b+3
=4b+−7+−15b+3
Combine Like Terms:
=4b+−7+−15b+3
=(4b+−15b)+(−7+3)
=−11b−4
Answer:

And if we find the indidivual probabilities we got:

And replacing we got:

Step-by-step explanation:
Previous concepts
A Bernoulli trial is "a random experiment with exactly two possible outcomes, "success" and "failure", in which the probability of success is the same every time the experiment is conducted". And this experiment is a particular case of the binomial experiment.
The binomial distribution is a "DISCRETE probability distribution that summarizes the probability that a value will take one of two independent values under a given set of parameters. The assumptions for the binomial distribution are that there is only one outcome for each trial, each trial has the same probability of success, and each trial is mutually exclusive, or independent of each other".
The probability mass function for the Binomial distribution is given as:
Where (nCx) means combinatory and it's given by this formula:
The complement rule is a theorem that provides a connection between the probability of an event and the probability of the complement of the event. Lat A the event of interest and A' the complement. The rule is defined by:
Solution to the problem
Let X the random variable of interest, on this case we now that:
For the first part we want this probability:

And if we find the indidivual probabilities we got:

And replacing we got:

Its simple what you do is you subtract not divide because if you where dividing you would be putting something into groups equally and not Addison because your not trying to find how much in all so it would be Subtraction another way is to see if there is how many more or How much more so if you see that then you know that its Subtraction! Hope this helps!:)
Umm could you maybe post a picture of the question?