Use the expression -2a / 1,000 where a represents the altitude in feet, to find the number of degrees fahrenheit at which the boiling point of water changes at an altitude of 5,000 feet

Abit confused about what you mean, but i think you might be referring to slope intercept form: y = mx + bin that case b, or the y intercept is already given.(0,-1)find the slope by using the formulay2 - y1/x2 - x1the final slope will be 4/2, equivalent to 2.now your equation should look like thisy = 4/2x -1sorry if this didn’t you out!