Net Magnetic Field at the Center of a Loop and X Distance Away From a Wire

[BornSurvivor]

Homework Statement

https://fbcdn-sphotos-a.akamaihd.net/hphotos-ak-prn1/553004_1959186995753_1725123128_934768_456680196_n.jpg
In case the words are too small:
I₂= 6.61I₁
The net magnetic field at center of loop is 0.
I'm looking for the radius of the loop

Homework Equations

for straight wire: B=(u₀*I)/(2\pi*r)
for loop: B= (u₀*I)/(2*r)

The Attempt at a Solution

So, since the two magnetic fields are perpendicular to each other: √(B₁²+B₂²)=0
I tried to find H in terms of R by using the right hand rule. I2/I1=(B2*H*\pi)/(B1*R) so H= -(6.61R/\pi)
But now I'm stuck, and I don't know if my work so far is even right.

 

[tiny-tim]

Hi BornSurvivor!

(pleeeeeease don't post such wide images! )

So, since the two magnetic fields are perpendicular to each other …

No, a loop current's magnetic field goes along the axis of the loop,

and a straight line current's magnetic field goes in loops around the line.