The heat index i is a measure of how hot it feels when the relative humidity is h (as a percentage) and the actual air temperature is t (in degrees fahrenheit). an approximate formula for the heat index that is valid for (t ,h) near (90, 40) is i (t, h) = 45.33 + 0.6845t + 5.758h − 0.00365t 2 − 0.1565ht + 0.001ht2 (a) calculate i at (t ,h) = (95, 50). (b) which partial derivative tells us the increase in i per degree increase in t when (t ,h) = (95, 50)? calculate this partial derivative.