Please, help, this is for my best friend! I will mark Brainliest.

Answer:
[tex]y = - \frac{3}{20} x + 900 \\ \\ y = - \frac{20}{3} x + 6000[/tex]
Step-by-step explanation:
[tex] \\ part \: a. \:( food \: expenses) \\ to \: solve \: these \: problems \: we \: surmone \\ \: the \: following \: laws : \to \\m = \frac{ y_{2} -y_{1} }{x_{2} - x_{1}} = \frac{815 - 812}{390 - 410} = - \frac{3}{20} = - 0.15 \\ the \: general \: slope \:i ntercept \: form \: is : \\ y = mx + c \\ to \: find \: c \: lets\: insert \: any \: two \: pairs \: for \: x \: and \: y \to \\ 812 = - \frac{3}{20} (410) + c \\ 16,240 = - 3(410) + 20c \\ c = \frac{1747}{2} \\ c = 873.5 \\ \\ therefore \: y = - \frac{3}{20} x + 900 \: (i.e \: to \: he \: nearest \: thousand). \\ \\ \\ part \: b. \: (medical \: expenses) \\ to \: be \: able \: to \: solve \: these \: problems \: we \: surmone \\ \: the \: following \: laws : \to \\m = \frac{ y_{2} -y_{1} }{x_{2} - x_{1}} = \frac{390 - 410}{815 - 812} = - \frac{20}{3} = - 6.667 \\ the \: general \: slope \:i ntercept \: form \: is : \\ y = mx + c \\ lets \: find \: c \: by \: insert \: any \: two \: pairs \: for \: x \: and \: y \to \\ 410 = - \frac{20}{3} (812) + c \\ 1230 = - 20(812) + 3c \\ c = \frac{17470}{3} \\ c = 5823.3333 \\ \\ therefore \: y = - \frac{20}{3} x + 6000 \: (i.e \: to \: he \: nearest \: thousand). \\ \\ [/tex]