What is an expression for vector x involving vector r, vector s, and vector t?

options are:

-2r - s + t
-3r + s - t
r + -3s - t
-r + s - t

Average acceleration: i have no idea how to do this.

Express in the simplest form: (x^2+9x+14/x^2-49) / (3x+6/x^2+x-56)

Starting at home, emily traveled uphill to the hardware store for 606060 minutes at just 666 mph. she then traveled back home along the same path downhill at a speed of 121212 mph. what is her average speed for the entire trip from home to the hardware store and back?