What is the value of a in the equation 5a – 10b = 45, when b = 3?

Here you go. Do you think that you could help me with my question

5a – 10b = 45 
5a – 10(3) = 45 
5a – 30 = 45 
+30 +30 
5a = 75/5 
a = 15

So Since we know what b equals. We can just plug it into the equation 
b = 3 
5a -10(3) = 45 

First step is to solve -10(3)  that means we multiply these two numbers. 
-10 x 3 = -30 
Now plug that in for what it was in the equation. 

5a - 30 = 45 

Now the next step is to add 30 to both sides to cancel out -30

5a - 30 = 45 
     +30 = +30
Now the 30's on the left side disappear and we solve on the right side. 
45 + 30 = 75 

Now set up your equation once again. 

5a = 75 

Now we divide both sides by 5 to isolate (or get a to be alone) 
5a = 75 
÷5 = ÷5 
the 5's on the left side disappear and we solve on the right side. 

75 ÷ 5 = 15 

So here's what we have left. 
a = 15 

Good Luck! :)