Answer:
40.5
Step-by-step explanation:
what i do is I divided first by 10. because 100 is 10x10.
so 4050 divided by 10 is 405.
405 divided by 10 is 40.5
By definition of the binomial coefficient,

so we have

as required.
If we're only counting 5 vowels (A, E, I, O, U) and 20 consonants (everything else, minus T), then there are

ways of picking the vowels, and

ways of picking the consonants.
We want the word to start with T, and we'll allow any arrangement of the other 4 letters, so that the total number of words is

Keep in mind that this means words like TRIES and TIRES are treated as different.
Answer is $506.25.
first month is $100,
second month is 100 times 1.5 which is 150.
thirst month is 150 times 1.5 which is 225.
fourth month is 225 times 1.5 which is 337.5
fifth month is 337.5 times 1.5 which is 506.25