Scientists plan to release a space probe that will enter the atmosphere of a gaseous planet. the temperature of the gaseous planet varies linearly with the height of the atmosphere. the delicate instruments on board completely fail at a height of 61.5 kilometers. what is the approximate temperature at this altitude?

You've told us only that the temperature varies linearly with altitude. 
That's very nice information, but you haven't given us the slope of
the linear variation, or any initial point. There's no way to answer
the question without those numbers.

It's really too bad about the delicate instruments failing and all that. 
But it sounds like they were working OK at some time before they
failed, so you must have received at least one good temperature
reading.  Tell us what that one was, and maybe we can work toward
an answer.

Alkaline earth metals are found in group 2 of the periodic table.