This is an arithmetic sequence with common difference -3. The nth term is first term + (n − 1) × difference = 7 + (10 − 1) × -3 = -20. An arithmetic sequence changes by the same amount each step. Use aₙ = a₁ + (n − 1)d, where a₁ is the first term, d is the common difference, and n is the term number. Do not multiply the common difference by n directly; there are only n − 1 jumps from the first term to the nth term. The correct answer is -20, which matches the calculation or reasoning shown.