Question 1008376
Linear relationship of points,  ( time, altitude )
Time units in minutes and altitude unit of feet


Described is (0, 12250) and slope  -450 feet per minute.
An unknown limiting point is some (x, 1900).


Slope-intercept form equation
{{{y=-450x+12250}}}


The described requirement is {{{y>=1900}}}
so  {{{-450x+12250>=1900}}}


{{{-450x>=1900-12250}}}

{{{x<=(1900-12250)/(-450)}}}

{{{highlight(x<=23)}}}