you can complete the square on x and y terms to find the radius:-
x^2 + 8x + y^2 - 22y - 88 = 0
(x + 4)^2 - 16 + (y - 11)^2 - 121 - 88 = 0
(x + 4)^2 + (y - 11)^2 = 121 + 88 + 16 = 225
(x + 4)^2 + (y - 11)^2 = 225
compare this with the standard form:-
( x - a)^2 + (y - b)^2 = r^2 where r = radius
So radius = sqrt225 = 15
Diameter = 2*15 = 30 Answer
