Final answer:
Ellie's package weighs 1 kilogram, and the cost to ship the package with either courier is $13.
Step-by-step explanation:
To find the weight of Ellie's package where the costs of two couriers are equivalent, we set up an equation where the two cost expressions are equal. Let x represent the weight of the package in kilograms.
The cost of the first courier is $10 + $3 per kilogram, so their cost expression is 10 + 3x. The cost of the second courier is $7 + $6 per kilogram, so their cost expression is 7 + 6x. To find the weight where the costs are the same, we set the two expressions equal to each other:
10 + 3x = 7 + 6x
Subtracting 3x from both sides, we get:
10 = 7 + 3x
Then, subtracting 7 from both sides, we get:
3 = 3x
Finally, dividing both sides by 3, we find that x is equal to 1:
x = 1 kg
Therefore, Ellie's package weighs 1 kilogram. To determine the cost for either courier, we substitute 1 kg back into any of the original cost expressions:
First courier: 10 + 3(1) = $13
Second courier: 7 + 6(1) = $13
Hence, the cost to ship the package with either courier is $13.