Current I1 and I2 flow in the wires shown in figure. The field is zero at distance x to the right of O. Then
x= I1I2a
x= I2I1a
x= I1−I2I1 + I2a
x= I1+I2I1 − I2a
μ0I14π a+x = μ0I24π a−xa−xa+x = I2I1I1a − I1x = I2a+I2xx= I1−I2I1 + I2a