1. 
 1 = 2.5 
2 = 5 
3 = 7.5 
4 = 10 
 
The n represents how many gallons of milk Mr. Yang is purchasing. 
 
F(6) would be 15. This value means it costs $15 for 6 gallons of milk. :)) 
 
2. 
f(1) = 1. 
 
The Common Difference is 5, since 11 + 5 = 16 and so on and so forth. 
 
The explicit rule is 
f(n) = 1n x 5
((If I got anything wrong on here, it would probably be the explicit rule. Sorry if it is incorrect!))