Here's a pattern to consider:
1+100=101
2+99=101
3+98=101
4+97=101
5+96=101
.....
This question relates to the discovery of Gauss, a mathematician. He found out that if you split 100 from 1-50 and 51-100, you could add them from each end to get a sum of 101. As there are 50 sets of addition, then the total is 50×101=5050
So, the sum of the first 100 positive integers is 5050.
Quick note
We can use a formula to find out the sum of an arithmetic series:

Where s is the sum of the series and n is the number of terms in the series. It works for the above problem.
(1) Snow fall in last week =
inches
Snow fall in today=
inches
Let us first change mixed fraction to improper fraction.

Now, make the denominators same.
, 
Now, find the difference between 14/4 and 23/4.
So, compared to last week
more inches of snow fell today.
(2) Given three times a number, minus nine, equals six times six, divided by four.
Let a number be X.
3X – 9 = 6 × 6/4
(3) To solve the equation:
3X – 9 = 6 × 6/4
3X – 9 = 36/4
3X – 9 = 9
3X = 18
X = 6