Apply right handed cork screw rule to determine the direction of the #vec B#
So,at point #A# i.e midway between the the two wire,magnetic field due to wire #1# is #-(2mu_0 i)/(4 piR)# direction is going into the plane of the page.
and for wire #2# it is #(2mu_0 i)/(4 piR)# as well but direction is coming out of the page of the plane,
So,magnetic field at point #A# is #(2mu_0 i)/(4 piR)-(2mu_0 i)/(4 piR)=0#
At point #B# magnetic field due to wire #1# is #B_1=(2mu_0 i)/(4 piR)# coming out of the plane of the page, and due to wire #2# it is #B_2=(2mu_0 i)/(4 pi*3R)= (mu_0 i)/(6 piR)# (as here distance is #R+R/2=(3R)/2#) direction is coming out of the plane of page.
So,net magnetic field at point #B# is #B_1 +B_2=B# (let)
Again,for point #C# due to wire #2# magnetic field #B_2' =-(2mu_0 i)/(4 piR)# direction is going into the plane of the page,and due to wire #1# it is #B_1'= -(mu_0 i)/(6 piR)# (compare for wire #2# effect on point #A#) and the direction is going into the plane of the page.
So,net magnetic field at point #C# is #B_1'+B_2'=B'#(let)
Clearly, #B=-B'# (direction is opposite of each other)
So,the ratio of magnetic field at point #A# ,#B# and #C# is #0:1:-1#