Let x be the number of friends.
He wants to give out 2x bars and have 10 left and he has 16 bars so the expression is:-
2x + 10 = 16
now he can solve for x to find the number of friends he can treat.
Given: 1 cm = 2 3/4 ft ; kitchen length = 4 1/2 cm
2 3/4 = 11/4; 4 1/2= 9/2
11/4 x 9/2 = 99/8 =12 3/8
OR You could use decimals
2 3/4 = 2.75 ; 4 1/2 = 4.5
2.75 x 4.5 = 12.375
12.375 = 12 375/1000 or 12 3/8