JEE Main 2020 Physics question

A wire of length L and mass per unit length kg is put under tension of 540 N. Two consecutive frequencies that it resonates at are : 420 Hz and 490 Hz. Then L in meters is -

• (A)2.1 mCorrect
• (B)1.1 m
• (C)8.1 m
• (D)5.1 m