Answer: 
 
2.50 + 5B ≤ 21; 
 
Step-by-step explanation: 
 
Cost of eggs = $2.50 
 
Cost of avocado = $5 (bag of 3) 
 
Total budgeted amount = $21 
 
Bags of avocado = B 
 
Therefore : 
 
(Cost of eggs + cost of avocado) ≤ total budgeted amount 
 
($2.50 + $5(B)) ≤ 21 
 
2.50 + 5B ≤ 21 
 
5B ≤ 21 - 2.50 
 
5B ≤ 18.50 
 
B ≤ 18.50 / 5 
 
B ≤ 3.7 
 
Therefore the maximum number of bags can purchase is 3(whole number without exceeding $21)