I think it is 568 if I’m not mistaken
Since each table had 7 women and 3 men at each table, that would mean each table has 10 people. Since there are 9 tables he was waiting on, and 10 people at each table, multiply 9 x 10, and you will find that he served 90 people in total.
Solution :
Let
be the unit vector in the direction parallel to the plane and let
be the component of F in the direction of
and
be the component normal to
.
Since, 


Therefore, 
From figure,

We know that the direction of
is opposite of the direction of
, so we have



The unit vector in the direction normal to the plane,
has components :


Therefore, 
From figure,

∴ 

Therefore,



According to given figure, The Triangle BDC is a right angled Triangle (Angle D = 90°)
So, we can apply Pythagoras theorem to find the Side a (Hypotenuse)
Now, let's solve ~
Therefore, Length of side a is 5 units ~