4 As part of an investigation, a chlorine block is immersed in a large tank of water held at a constant temperature. The block slowly dissolves, and its weight, \(y\) grams, is noted \(x\) days after immersion. The results are shown in the table.
| \(\boldsymbol { x }\) days | 5 | 10 | 15 | 20 | 30 | 40 | 50 | 60 | 75 |
| \(\boldsymbol { y }\) grams | 47 | 44 | 42 | 38 | 35 | 27 | 23 | 16 | 9 |
- Calculate the equation of the least squares regression line of \(y\) on \(x\).
- Hence estimate, to the nearest gram, the initial weight of the block.
- A company which markets the chlorine blocks claims that a block will usually dissolve completely after about 13 weeks. Comment, with justification, on this claim.
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