The average of the numbers $$a, b, c, d$$ is $$(b + 4)$$. The average of pairs $$(a, b)$$, $$(b, c)$$ and $$(c, a)$$ are respectively 16, 26 and 25 . Then the average of $$d$$ and 67 is

The pair averages give $$a + b = 32$$, $$b + c = 52$$ and $$c + a = 50$$, so adding them, $$2(a + b + c) = 134$$ and $$a + b + c = 67$$. Hence $$a = 15$$, $$b = 17$$ and $$c = 35$$. The average of the four numbers is $$b + 4 = 21$$, so $$a + b + c + d = 84$$ and $$d = 84 - 67 = 17$$, making the average of $$d$$ and 67 equal to $$\frac{17 + 67}{2} = 42$$.