we have that
The formula for food cost percentage (FCP) given selling price (SP) and food cost (FC) is FCP = FC/SP x 100
so
in this problem we have
FCP=20%
FC=$2.60
substitute given values
20=(2.60/SP)*100
0.20=2.60/SP
SP=2.60/0.20
SP=$13
the answer is $13