calculus question

for a rectangle with length l and width w, its area A = lw and perimeter P = 2l + 2w.

(a) for a rectangle with length l = 5.4 and width w = 3.7, estimate the change in A as a linear function of the change in l and the change in w.
(b) let the perimeter-to-area ratio R = P/A. express R as a function of l and w. hence, for a rectangle with length l = 5.4 and width w = 3.7, find its perimeter-to-area ratio R and estimate the change in R as a linear function of the change in l and the change in w.
(c) based on the results in parts (a) and (b) above, for a rectangle with length l = 5.4 and width w = 3.7, if you want to have its perimeter-to-area ratio R decreased by 0.0003 but maintain its original area, how should you adjust the length l and the width w?

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need steps and exlanation briefly. thanks!!!