120+x=460

x=340

x+89=689

x=600

540+x=800

x=260

770-x=540

x=230

x-430=560

x=990

870-x=70

x=800

1. 120 + х = 460

460 - 120 = 340

х = 340

2. х + 89 = 689

689 - 89 = 600

х = 600

3. 540 + х = 800

800 - 540 = 260

х = 260

1. 770 - х = 540

770 - 540 = 230

х = 230

2. х - 430 = 560

560 + 430 = 990

х = 990

3. 870 - х = 70

870 - 70 = 800

х = 800