Answer:
$500
Step-by-step explanation:
You want the cost of a 50 cm square tile if a 30 cm square tile costs $180 and cost is proportional to area.
Cost
If c represents the cost of the larger tile, cost being proportional to area means ...
c/50² = 180/30²
c = (50²/30²)·180 = 500
The cost of the other tile is $500.
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Additional comment
The area is the square of the edge length.
