A teacher is preparing party favors for her students and wants to personalize the gifts according to their preferences. She surveys her class and finds that out of 30 students, 18 prefer superhero-themed favors and 12 prefer princess-themed favors. The store sells packs of 6 superhero-themed favors for $4 per pack and packs of 4 princess-themed favors for $3 per pack. Additionally, the store sells individual superhero-themed favors for $1 each and princess-themed favors for $0.75 each. What is the minimum amount the teacher can spend to buy the exact number of favors each student wants? Let's think step by step and output the final answer within \boxed{}.
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