B1=μₒ•I1/2•π•r1 =4π•10^-7•30/2•π•0.15 =4•10^-5 T,
B2=μₒ•I2/2•π•r2 =4π•10^-7•40/2•π•0.25 =3.2•10^-5 T.
Generally there are two points which are separated by given distances from I1 (point M) and I2 (point N), where we have to find magnetic field B. They are above and below MN line.
Let us examine the point P which is below the line connecting I1 and I2.
Let the left current I1 be directed into the page,
and the right current I2 be directed out of the page.
B1 is normal to MP line and is directed due to west,
B2 is normal to NP line and is directed south east.
Net B is directed southwest.
The magnutude of B may be found using cosine law.
The angle α is equal to the angle MPN which cosine is
cosα=15/25=0.6.
B=sqrt(B1²+B2²-2B1•B2•cosα) =
=10^-5•sqrt[ (4²+3.2²-2•4•3.2•0.6)]= 3.3•10^-5 T.
If I1 is out of the page and I2 is into the page,
net B is directed northeast and is of the same magnitude.