How to solve a quadratic in a non quadratic form

How to Solve a quadratic equation in a non quadratic form such as :

s² + 2abs + b² s = 4

a = 5

b = 2

Do I solve the solution by completing the square?

My tutor has advised me to substitute some values into the equation which I have done shown above, with these values it = 100

He said also to re arrange and maybe move the b² to the right hand side s² + 2abs = -b²

Do you know why he has advised me to do this?

As you can see im kinda hitting a brick wall with this quadratic so any help would be much appreciated :O)

Richard