How do u work out weight c and d and what r the answers

The whole secret of things that are balanced on a pivot like this is:

The sum of all of the 'moments' is equal on both sides.

The moment of each weight is  (the weight) times (its distance from the pivot). 
If you add up those for each eight on one side, it has to be equal to the sum
of all the ones on the other side.

2. a). 
The moments on the right side are:  (4 x 0.15) and (1 x 0.40).
They add up to  (0.60 + 0.40) = 1.00

The only moment on the left side is  (C x 0.25).  Both sides have to be equal.

C x 0.25 = 1.00

Divide each side by 0.25, and you have    C = 4 N .



2. b).
The only moment on the left side is  (5 x 0.40) = 2.00

The moments on the right side are (1 x 0.20) and (D x 0.30)
They add up to  (0.3D + 0.2).

Both sides have to be equal.    0.3D + 0.2 = 2.0

Subtract 0.2 from each side:      0.3D  =  1.8

Divide each side by 0.3:                D = 6 N