The wires P and Q carry current in same direction, therefore they attract each other. The force on R due to P is towards the wire P and is given by,
FRP=
μ0
4π
×
2iP×iR
rPR
×I =
10−7×2×10×10
0.10
×0.15N PRP=3×10−5N [towards left] Similarly, wires Q and R attract each other as they also carry the current in the same direction. The force on R due to current in Q is towards right hand side. Therefore the force on R, due to Q, is given by FQR=
μ0
4π
.
2iQiR
rQR
I=
10−7×2×20×10×0.15
0.10
FQR=6×10−5N [towards right] ∴ Net force on R is F=6×10−5−3×10−5N =3×10−5N [towards right (Q)]