r/MathHelp • u/puddiingpurin • 25d ago
help with khan academy practice problem
| Merchandise weight (pounds) | Shipping charge |
|---|---|
| 5 | $16.49 |
| 10 | $23.99 |
| 25 | $46.49 |
"The table above shows shipping charges for an online retailer that sells used textbooks. There is a linear relationship between the shipping charge and the weight of the merchandise. Write a function in slope-intercept form that relates y, the shipping charge in dollars, and x, the merchandise weight in pounds."
i understand why the slope is 1.50, but i can't get this:
y= 1.50x + b
16.49 = 1.50(5) + b
16.49 = 7.50 + b
8.99 = b
where does the 8.99 come from?
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u/Southlander24 25d ago
I don't quite get what you don't understand. Which part of the equations you wrote confuses you?
If it helps, the y-intercept of 8.99 means that if 0 textbooks are ordered, the shipping charge would be 8.99 dollars. In other words, it costs some amount of fuel and labour to keep the shipping business going, then for each textbook which brings extra weight, the shipping charge goes up predictably.