Average mass of d,k,l 42 .D is 6 kg heavier than average mass of k and l .k is 6 kg heavier than l. Find mass of d

what do we know?

(d+k+l)/3 = 42
d = 6+(k+l)/2
k = l+6

So, start substituting:

d+l+6+l = 126
2d = 12+l+6+l
or,

d+2l = 120
2d-2l = 18

Add these to get

3d = 138
d = 46