Answer:
a. 

b. x = 10
Explanation:
a. The number of home runs hit by Jack last season = x
It is given that Henry hit 3 more than half as many home runs as Jack hit.
Half of the runs hit by Jack = 

3 more than half the runs = 

So, the number of home runs hit by Henry = 

But, it is given that Henry hit a total of 8 runs.
Therefore, 

b. 

Subtract 3 from both sides.
 

= 5
x = 5 × 2
= 10
Hence, Jack hit 10 runs in the last season.