Răspuns :
x=primele timbre
x×2+40=180 (timbre)
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x+x=?
x+x×2+40=180
x+2x+40=180
3x+40=180
3x=180-40
3x=140
x=140÷3
x=40 (a avut la inceput)
x×2+40=180 (timbre)
-----------------------
x+x=?
x+x×2+40=180
x+2x+40=180
3x+40=180
3x=180-40
3x=140
x=140÷3
x=40 (a avut la inceput)