Find a number between 9/16 and 21/32.

9/16 = (2*9)/(2*16) = 18/32

We need to find number between 18/32 and 21/32.

Since 18/32<19/32<21/32 one such number is 19/32.

A slope of -3 means that for every horizontal change of 1, there is a vertical change of   -3  

slope = change in y / change in x

change in y = slope*change in x

change in x = 1

slope = -3 

change in y = the vertical change

change in y = (-3)*1

change in y = - 3