The first term of an arithmetic sequence is 4 & the tenth term is 67 what is the common different?

Based on what i know about mean, this doesn't add up.

Agrain trader buys the following amounts from three suppliers: 3,200 pounds, 5,100 pounds and 700 pounds. what is the total weight of his purchase?

Given the sequence 7, 14, 28, 56, which expression shown would give the tenth term? a. 7^10 b. 7·2^10 c. 7·2^9