How do you solve these algebra problem?

You solve for x by reversing all the operations surrounding x, from the outside in.

3x+xy=8

First, we need to get a single x on one side.

Use the distributive law:

x(3+y) = 8

Now, the outermost operation is multiplying by (y+3).

We apply the inverse operation: *divide* both sides by (y+3):

x = 8/(y+3)

... and we're done.

Now, can you apply those principles to the first one?