In the second week, Hannah will save $4 x 2 = $<<4*2=8>>8.
In the third week, she will save $8 x 2 = $<<8*2=16>>16.
In the fourth week, she will save $16 x 2 = $<<16*2=32>>32.
Her total savings for a month will be $4 + $8 + $16 + $32 = $<<4+8+16+32=60>>60.
Hannah needs to save $80 - $60 = $<<80-60=20>>20 in the fifth week.
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