Answer:
X < 10
where X is the weight of the package in pounds
The package should weigh less than 10 pounds for Ship4U to be the cheaper option
Step-by-step explanation
Let the weight of the package be X pounds
Cost of shipping by Post Office = 9 + 0.5X
Cost of shipping by Ship4U = 6 + 0.8X
For Ship4U to be the cheaper option
6 + 0.8X < 9 + 0.5X
Subtract 6 on both sides and subtract 0.5X from both sides:
0.8X - 0.5X < 9 - 6
0.3X < 3
Divide by 0.3 on both sides
0.3X/0.3 < 3/0.3
X < 10
The package should weigh less than 10 pounds for Ship4U to be the cheaper option
At a weight of 10 pounds, both shipping costs are the same
Post Office cost for 10lb package = 9 + 0.5(10) = 9 + 5 = $14
Ship4U cost for 10lb package = 6 + 0.8(10) = 6 + 8 = $14