Correct Answer - Option 3 : 520

The ratio of first and second number is 6 : 7

The ratio of second and third number is 8 : 9

After combine both we get,

⇒ 6 : 7 : : 8 : 9

⇒ 48 : 56 : 63 ⇒ **48x, 56x and 63x.**

The given difference of first and third is = 150

⇒ 63x - 48x = 150

⇒ 15x = 150

⇒ x = 10

put the value of x we get,

First number = 48x = 48 x 10 = 480

Second number = 56x = 56 x 10 = 560

Third number = 63x = 63 x 10 = 630

Average of First and second number we get,

(480 + 560)/2 = 1040/2 = **520**

Hence,** "520" **is the correct answer.