Please help me im very behind

-1

We are given:

a₁ = -17    

a₁₃ = -29

Solving for the Common Difference (d):

We know that the formula for an AP is:

aₙ = a₁ + (n-1)d

The formula for the third term will be:

a₁₃ = a₁ + (13 - 1)d

replacing the given values:

-29 = -17 + (12)d

-12 = 12d                            [adding 17 on both sides]

d = -1                                 [dividing both sides by 12]

Hence, the common difference is -1

answer is  

c.

56

hope you get this right