(1)x+6=12.5,
x+6-6=12.5-6,
x=6.5;
(2)2.5x-x=1.8,
1.5x=1.8,
1.5x÷1.5=1.8÷1.5,
x=
6
5 ;
(3)(4.5+x)×2=13,
(4.5+x)×2÷2=13÷2,
4.5+x=6.5,
4.5+x-4.5=6.5-4.5,
x=2;
(4)2x-2.5×10=75,
2x-2.5×10=75,
2x-25=75,
2x-25+25=75+25,
2x=100,
2x÷2=100÷2,
x=50.
(1)x+6=12.5,
x+6-6=12.5-6,
x=6.5;
(2)2.5x-x=1.8,
1.5x=1.8,
1.5x÷1.5=1.8÷1.5,
x=
6
5 ;
(3)(4.5+x)×2=13,
(4.5+x)×2÷2=13÷2,
4.5+x=6.5,
4.5+x-4.5=6.5-4.5,
x=2;
(4)2x-2.5×10=75,
2x-2.5×10=75,
2x-25=75,
2x-25+25=75+25,
2x=100,
2x÷2=100÷2,
x=50.