Final answer:
The total cost of the slacks and boots, before sales tax, is $149.80.
Step-by-step explanation:
To find the total cost of the slacks and boots, we need to add the price of the slacks ($59.90) to the price of the boots ($89.90).
$59.90 + $89.90 = $149.80
The total cost of the slacks and boots, before sales tax, is $149.80.