Explain this I think I have done it wrong

The weights W (in kg) of a number of women at the age of 21 are shown plotted against their birth weight B (in key Also shown is the line of best fit. (4 marks) 65 60 55 (kilograms) Weight at 21 years 50 45 40 + 1.5 2 2.5 3.5 4 4.5 W45 + 3.5x Birth weight (kilograms) a Find the equation of the line of best fit and write it in terms of W and B. Round the y-intercept and slope values to 3 significant figures. W 45 + 3.5x 2 marks b Use your equation to complete the following sentence by filling in the blank space: The equation of the line of best fit tells us that, on average, for each additional kilogram in birth weight, a woman's weight increased by _3 . 5 kg. 1 mark Use the equation to predict the weight of a woman whose birth weight was 3 kg. Rounded to 1 decimal place. 55. 5 xg 1 mark