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.