Use the distance formula: d = √[ (x2 - x1)² + (y2 - y1)² ]
(x1, y1) = (-1, 5) ---> x1 = -1 y1 = 5
(x2, y2) = (0, 4) ---> x2 = 0 y2 = 4
---> d = √[ (x2 - x1)² + (y2 - y1)² ]
---> d = √[ (0 - -1)² + (4 - 5)² ]
---> d = √[ (1)² + (-1)² ]
---> d = √[ 1 + 1 ]
---> d = √2
.... finish this with a calculator ....