Answer: There are 50 adult-size shirts that were sold .
Step-by-step explanation:
Since we have given that
Cost of adult-size shirts = $20
cost of child-size shirts =$15
Let hte number of adult-size shirt be x
Let the number of child-size shirt be y
According to question,

So, we will use "Substitution method" :

Put this value in equation (1):

So, put the value of y in x :

Hence, there are 50 adult-size shirts that were sold .