If the lines 3x + 4y - 14 = 0 and 6x + 8y + 7 = 0 are both tangents to a circle, then its radius is

Given lines 
$3x+4y-14=0\to \left(1\right)$
$6x+8y+7=0\to \left(2\right)$           
Given lines are parallel 
Radius = $\frac{1}{2}$ (distance between parallel lines)  =$\frac{1}{2}\left(\frac{7}{2}\right)=\frac{7}{4}$