Hi i really need with a and b. you

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!