On a balance scale, six spools and one thimble balance thirteen buttons. also, one spool balances one thimble and one button. how many buttons will balance one spool?

First write the equation:
#1- six spools and one thimble balance thirteen buttons: 6S+1T=13B
#2- one spool balances one thimble and one button: 1S=1T+1B

Take the first equation and make it so you can substitute it in the second so we look for an alike variable 1T so the first equation is rearranged like this 1T=13B-6S Then we place it in the second equation like this:
1S=(13B-6S)+1B then we simplify
1S+6S=13B+1B
7S=14B
S=7B
So one spool will balance seven buttons
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