This is worth a lot of points and i’m

Is that a math question or a novel?

Inside.  Let d be the depth in km and t be the temperature in C at that depth.  We have an initial temperature of 15 C and an increase of 25 degrees C per km.  Our model is thus

t = 15 + 25d

or in slope intercept form

t = 25d + 15

At d=10 we expect a temperature of 265 C.

At d=40 we expect a temperature of 1015 C

Our range is 265 C to 1015 C, span of 750 C

Outside.  Same story, different slope.  d is now the altitude in km, Here we have a decrease of 6.5 C per km, so that's a negative slope.  Our model is

t = 15 - 6.5d

t = -6.5d + 15

At d=8 we get t= 15-6.5(8) = -37 C

At d=20 we get t=15-6.5(20) = -115 C

Range -115 C to -37 C, span of 78 C

yes because there is exactly one y value for every x value

for function there can't be more than one value for every x value