How to solve this

Question

If the dewpoint D on the ground is 50 Fahrenheit in the dewpoint X miles high is given by D(x)= 50-5.8 X find the attitudes or the dewpoint ranges from 41.3 Fahrenheit to 29.7 Fahrenheit.

Answer 1

Question is somewhat confusing to read, but it looks like the dewpoint varies linearly with altitude in miles.

D(x) = 50 - 5.8x where x is altitude. Slope is negative 5.8, so dewpoint is reduced by 5.8º for every mile above ground level.

To find altitude corresponding to 41.3º, plug in 41.3 for D(x) and solve for x. Do same for 29.7º.

Answer 2

41.3 = 50 - 5.8x₁, solve for x₁

29.7 = 50 - 5.8x₂, solve for x₂

The dewpoint ranges from x₁ to x₂