For: rate=k[a]^x determine the value of x if the rate doubles when [a] is doubled; and if the rate quadruples when [a] is doubled.,

1. The value of x if the rate doubles when [A] is doubled is that x = 1 

2. Then if the rate quadruples when [A] is doubled is that x= 2
Since x=1 when the rate doubles, so if it quadruples, it will be times 2.
So the solution to this is 1 times 2= 2
x=2

The answer is true for your question.

The phase where ice changes directly to gas is called sublimation