Question

6х+12у-42=0, если у=0

Answer 1

6x+12*0-42=0
6x+0-42=0
6x-42=0
42+0=42
42:6
x=7

Answer 2

$6x + 12y - 42 = 0 \\ 6x + 12 - 0 - 42 = 0 \\ 6x + 12 - 42 = 0 \\ 6x - 30 = 0 \\ 6x = 30 \div 6 \\ x = 5$