see the attached figure below to better understand the problem
In this problem, we have an isosceles triangle
the measure of the other two interior angles are
2A+64 10'=180
2A=115 50'
115 50'------> convert to degrees
115+50/60=115.83 degrees
2A=115.83
A=57.92 degrees
Now we have the right triangle
tan(57.92)=x/2.100
x=2.100*tan(57.92)
x=3.35 in