To solve the problem given in the figure attached, you must apply the proccedure shown below:
 1. You have the following expression given in the problem:
 x^19 = y
 2. By definition, you have:
 logb(x)=y
 b^y=x
 3. Therefore, you have:
 
 x^19 = y
 logx(y)=19
 4. Then, as you can see, the answer is:  logx(y)=19