A pure substance that is made of only one kind of atom is called an element.
An element is a pure substance, which means it is made up of only ONE kind of atom.
You want to undo the (-9 1/2), so you will add 9 1/2 to each side
Step-by-step explanation:
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100°+(4y+25)+(3y+20)=180°
100+4y+25+3y+20=180
7y+145=180
7y=35
y=5
100°; 45°; 35°