#1**+1 **

Let the number of strawberry sold = x

The number of vanilla = strawberry + 2 = x + 2

The number of chocolate = vanilla + 11 = (x + 2) + 11 = x + 13

So we have that

x + ( x + 2) + ( x + 13) = 42 simplify

3x + 15 = 42 subtract 15 from both sides

3x = 27 divide both sides by 3

x = 9 = strawberry sold

CPhill Jan 29, 2019