The amount of money that Charlie saves each week is directly proportional to the amount he earns. Last week Charlie saved $32 on his earnings of $512. At the same rate, how much will Charlie save this week on his earnings of $448?

if k is a constant of proportionality then we know from last week that
512= k ·32 so k=512/32=16;

This week 
448= k · amount he saved
448=16· amount he saved
amount saved=448/16=28

Answer $28