A) To solve this equation, you would need to fill in the blank with a substitute. Let x represent the unknown number. 

 = 

Next, you would cross multiply. 
135 = 45x
Now, the last step would be to isolate the x. To do this, you would divide both sides by 45. 
3 = x =
 = 
b) To solve this equation, you would need to fill in the blank with a substitute. Let x represent the unknown number. 

 = 

Next, you would cross multiply. 
18 = 2x
Now, the last step would be to isolate the x. To do this, you would divide both sides by 2. 
9 = x =
 =
I hope this helps!