We can find the average speed of the body by finding the total distance covered, and then dividing it by the total time of the motion.
The total distance covered is:
[tex]S=30 m + 45m+65m=140 m[/tex]
while the total time of the motion is
[tex]t=5 s+7s+5 s=17 s[/tex]
So, the average speed of the body is:
[tex]v= \frac{S}{t}= \frac{140 m}{17 s}=8.24 m/s [/tex]