a) 7x = 3x = 100
12x - x = 121
15x - 6x -x =64

б) 9х + х - 2х =8
17х - 7х +3х =169
20х + х 16х = 265

7x-3x=1004x=100x=100÷4=2512x-x=121 11x=121x=121÷11=1115x-6x-x=648x=64x=64÷8=89x+x-2x=8 8x=8x=8÷8=117x-7x+3x=16913x=169x=169÷13÷1320x+x-16x=2655x=265 x=265÷5=53

7х-3х=100; 4х=100; х=100÷4; х=25. 12х-х=121; 11х=121; х=121÷11; х=11. 15х-6х-х=64; 8х=64; х=64÷8; х=8. 9х+х-2х=8; 8х=8; х=8÷8; х=1. 17х-7х+3х=169; 13х=169; х=169÷13; х =13. 20х+х-16х=265; 5х=265;х=265÷5; х=53.