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The bricklayer estimated that 500 bricks would be needed for that wall.
Literal
Bricklayer [topic-は] that wall [location-には] 500 bricks [subject-が] necessary [quotative-と] estimated.
The quotative と marks what was 'estimated' — the complement clause その塀には５００個のレンガが必要だ. Inside that clause, には stacks location + topic ('for that wall, as far as it's concerned'). The counter 個 is the generic 'small object' classifier, fitting for individual bricks. 見積もる specifically means to estimate cost, quantity, or extent — a practical, commercial verb.