Please see the diagram.

Mass of blade = m kg. Mass of handle is M. kg Mass of spade = M+m. kg

We balance the moments of mass/weights, using products of arm lengths to the centers of masses and masses.

from the top figure,

[ (30/L)m ] * 15 = [(L-30)/L * m ] * (L-30)/2 + M * (20 + L/2)

900*m = m (L-30)² + M *(40+L) L

60 m = 40 M + (m+M) L --- (1 )

from the next diagram, we get:

(50 - L/2) m + (50-L)/2 * [(50-L)*M/(100-L)] = 2 *50 + 25 * [ 50*M/(100-L) ]

so we get,

(100-L) [100 m - L m - 200 ] = M (100 -L ) L

100 m = 200 + (m+M) L

using --(1) we get

100 m = 200 + 60 m -40 M

40 (M+m) = 200

M+m = total weight of spade = 200/40 = 5 kg