It is known that a mathematical symbol △ holds the following equation: 2 △ 4 = 8, 5 △ 3 = 13, 3 △ 5 = 11, 9 △ 7 = 25, then 7 △ 3=______ .

It is known that a mathematical symbol △ holds the following equation: 2 △ 4 = 8, 5 △ 3 = 13, 3 △ 5 = 11, 9 △ 7 = 25, then 7 △ 3=______ .

7 △ 3 = 7 × 2 + 3 = 17