what does it mean when the variable (a) is in an equation? Example: 3+2a-1+4a

It's just another number that happens to have a letter in it. You can't melt letters and numbers together, though, so all you can do is simplify the equation, but it's not going to be a single number.

3+2a+1+4a

3+1 and 2a+4a

4+6a ... this is the farthest we can go.

that means that the variable (a) is a random number and you need to know what the variable equals to finish the problem.

You would need a value for a such as a = 1 to solve it entirely.

However, we can simplify 3 + 2a - 1 + 4a to:

3 - 1 + 2a + 4a

2 + 6a

or 6a + 2.

DragonSlayer554    gave a really good answer to a question like this just a day or two ago.

Where is THE Dragon when you need him.   Off fighting for Camelot I expect!  I should not complain, we need our valiant defender!