Answer
$B=0.9478096$
Work Step by Step
We know that:
$\gamma=\frac{\Delta t}{\Delta t_{\circ}}$
We plug in the known values to obtain:
$\gamma=\frac{6.90}{2.20}=3.1364$....eq(1)
We also know that
$\gamma=\frac{1}{\sqrt{1-B^2}}$....eq(2)
Comparing eq(1) and eq(2) we obtain:
$3.1364=\frac{1}{\sqrt{1-B^2}}$
After simplification, we obtain:
$B=0.9478096$
