Net force = T - mg where T is the tension in the line, m is the mass of the fish and g = 9.8 is the acceleration due to gravity.

But net force = ma = m(4.5).

Therefore 4.5 m = T - 9.8m => 14.3 m = T.

The maximum value of T is 22N. If the line snaps, then T > 22N.

Therefore 14.3 m > 22 => m > 22/14.3 = 1.5 (correct to 1 decimal place).