For find f(-2) of f(x)=7x+3, plug in -2 for x.
7(-2)+3=y
-14+3=y
y=-11
To find the rate, or the slope, you divide x/y. So 2/6 is 1/3. 3 over 9 is also 1/3. So the rate is 1/3. In rates you always divide, you don't mulitply or subtract or add to find the rate.