Analyzing the functions of each variable and statement in the program,

According to the sequence shown in the flow chart, it can be seen that:

The function of this program is to compare f (x)=2x and g(x)=x2 function values,

and output the maximum value among them.

When x=3, f(3)=23=8, g(3)=32=9,

∵9>8,

∴h(3)=9．

So the answer is: 9