Answer:
.409 N
Step-by-step explanation:
For this to balance, the moments around the fulcrum must sum to zero.
On the left you have .21 ( is that down? I will assume it is) 
 Counterclockwise moments :
 .21 * 40 + 1.0 * 20 
 Clockwise moments :
 .5 * 20 + F * 45 
these moments must equal each other 
.21*40 + 1 *20 = .5 * 20 + F * 45 
 F = .409 N