Radius of the mohrs circle

Question

The state of stress at a point under plane stress condition is
$\sigma _{xx}$ = 40MPa, $\sigma _{yy}$= 100MP and $\tau _{xy}$ = 40MPa.

The radius of the Mohr’s circle representing the given state of stress in MPa is
(a) 40                       (b) 50
(c) 60                        (d) 100