Dear aspirant,

This is a formula based question and you need to follow the formula and make equations and need to solve the equations by substituting.

So, R^2= A^2 +B^2 + 2.A.B. cos theta

In the first case theta is 90 degree so it will be zero so the final equation becomes A^2+ B^2 = 100 KN.

Then use the second case and the same formula where theta is 60 degrees to get an equation in terms of A and B.