If the sum of interior angles and the sum of exterior angles of a polygon differ by $540°$, then the number of sides of the polygon is

Sum of interior angles $-$Sum of exterior angles of a polygon $=540°$

$(n-2)180-360°=540°$

$(n-2)180=540°+360°$

$(n-2)180=900°$

$(n-2)=\frac{900°}{180}$

$(n-2)=5$

$n=5+2$

$\therefore n=7$