Factors of 24: 1,2,3,4,6,8,12,24
factors of 30: 1,2,3,5,6,10,15,30
factors of 42: 1,2,3,6,14,21,42
Answer: draw a dot at -7 on the x-axis and a dot at positive 7 on the y-axis. then draw your line through the dots and across the graph using a ruler or just try drawing a straight line.
The answer without a doubt is 69/420