here's the equation: x+x+(x+12)+ 1/2(x+12) =81
combine like terms
(x+x+x+1/2x) + (12+6) = 81
simplify
7/2x +18=
subtract 18 from both sides.
7/2x=63
multiply by reciprocal (aka 2/7)
x=18
18+12=30 so celia gave 30.
Hope this helps!
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