Create an arithmetic sequence with a common difference of -10

0, -10, -20, -30, -40, -50, ..., -10(n-1)

Step-by-step explanation:

An arithmetic sequence with a common difference of -10 just indicates that each term adds negative ten to the prior one, which is just subtracting ten.  If you slap a random value as the beginning, zero in my example, then you spam subtract negative tens, you get an arithmetic sequence.  The variable "n" is just the term number - 0 was n=1, -10 was n=2, -20 was n=3, etc.

a = 11 : 4

b = 38

c = 1 for every 6

30 units^2

step-by-step explanation:

area is l × w

the length is 3

and the width is 10

3 × 10= 30 units squared