Answer:
$433.50
Step-by-step explanation:
You want the commission on $8400 in sales if the rate is 4.5% for the first $4500, 5.0% for the next $1500, and 6.5% for amounts above that.
The calculation figures the amount of commission in each sales bracket, and adds them up. It can be written as ...
C = 0.045×4500 +0.05×1500 +0.065×(8400 -4500 -1500)
= 202.50 +75.00 +156.00
= 433.50
Her commission is $433.50 on $8400 worth of sales.
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Additional comment
For amounts above 6000, this can also be written as ...
C = .045(4500) +.05(6000 -4500) +.065(x -6000)
= 4500(.045 -.05) +6000(.05 -.065) +.065x
= -22.50 -90.00 +.065
= 0.065x -112.50
Then for x = 8400, the commission is 6.5(84) -112.50 = 433.50.