Hi there!
There are two steps to take when solving this equation, but before we even think about that, let's start by rewriting the equation.
5a + 17 = 47
Step 1) Subtract 17 from both sides.
5a + 17 - 17 = 47 - 17
5a = 30
Step 2) Divide both sides by 5.
5a/5 = 30/5
a = 6
So, your final answer therefore is
a = 6
Hope this helps!
TIP - This method can be used when solving any equation with 1 variable. :D