Answer:

Step-by-step explanation:
The sum of N consecutive natural numbers is given by:

We need to find the sum of the natural numbers between 12 to 38.
To calculate the required sum we have F=12, L=38, but we don't have the value of N.
From 12 to 38 there are 38 - 12 + 1 = 27 natural consecutive numbers, thus N=27.
Substituting in the formula:




The answer is C: 3x + 30 = 11x.
Hope my answer helped!! It would really help me if you gave me Brainliest Answer!!
He could buy 12 postcards for $3.36.
and 8 letters for $3.36