Can someone teach me how to do this?

the formula is a_{1}+(n-1) d

so a_{1} would be the first number in the sequence, which would be 13 in problem 9.

13+(n-1)d

then you put in n, which is 10 (it represents which number in the sequence you're looking for, for example 16 is the second number in the sequence)

13+(10-1)d

then you find the difference between each number, represented by d which in this case is 3

13+(10-1)3

13+(9)3

13+27=

40

a.   since the profit made in 2012 is equal to the profit made in 2014, the profit is symmetric about the line y = 120,000.

step-by-step explanation: