Correct Answer - Option 3 : 8.75

**Given **

33x - y = 81

3^{x + y} = 729

**Formula/ Concept used**

If a^{m + n} = a^{p} then m + n = p

where m, n and p are real numbers.

**Calculation**

33x - y = 3^{4}

3x-y = 4 ......(1)

3x + y = (3^{2})^{3}

x + y = 6 ......(2)

on adding equation (1) and (2)

4x = 10

x = 2.5

put x= 5 in equation (2)

y = 6 - x

y = 6 - 2.5 = 3.5

∴ x × y = 2.5 × 3.5 = 8.75