The correct expression is:
(2×7)-(3×1)
Explanation:
The expression for doubling 7 is multiplying 7 by 2, or 2×7.
The expression for the product of 3 and 1 is 3×1.
Subtracting the second number from the first one would be writing the first number first, then minus the second: (2×7)-(3×1)