To determine how many people attended the birthday party, we can use the linear function model given for the total cost \( b(x) = 100 + 15x \), where \( x \) is the number of people attending (excluding Leslie and Steve).
Leslie received a bill of $550. We need to set the function equal to this amount and solve for \( x \):
\[ b(x) = 550 \] \[ 100 + 15x = 550 \]
Now, we can solve for \( x \):
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Subtract 100 from both sides: \[ 15x = 550 - 100 \] \[ 15x = 450 \]
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Divide both sides by 15: \[ x = \frac{450}{15} \] \[ x = 30 \]
So, \( x = 30 \) represents the number of people attending in addition to Leslie and Steve.
Since Leslie and Steve are also attending, we need to add them to this number:
\[ \text{Total number of attendees} = x + 2 = 30 + 2 = 32 \]
Thus, the total number of other people who attended the birthday party, excluding Leslie and Steve, is 30.