//chapter 2
//example 2.12
//page 53
printf("\n")
printf("given")
disp("A")
trr=10*10^-9;
tf=10*trr*10^9
printf("minimum fall times is %dns\n",tf)
disp("B)")
trr=3;
tf=10*trr;
printf("minimum fall times is %dns\n",tf)