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Math·Algebra·Linear functions

hard

A dance studio charges an introductory fee for the first $3$ lessons and then charges a fixed fee for each additional lesson. One student took $4$ lessons and was charged $60. Another student took $16$ lessons and was charged $300. Which function $f$ gives the total charge, in dollars, for any student who took $x$ lessons, where $x>3$?

A

$f(x)=15x$

B

$f(x)=15x+60$

C

$f(x)=20x$

D

$f(x)=20x-20$