A)13+7x=2x+12
7x-2x=12-13
5x=-1
x=-5
б)2(x-5)+3=x
2x-10+3=x
2x-x=10-3
x=7
75/100=3/4
75/25=3/1=3
48/63=16/21
56/60=14/15
35/42=5/6
36/32=9/8
81/420=27/140
42/49=6/7
72/24=12/4=3
32/60=8/15
48/12-7/12+11/6+7/3+5/4=41/12+22/12+28/12+15/12=63/12+28/12+15/12=
=78/12+28/12=106/12= 8 10/12.