Substitution method
4a=4-b
4a=5-b
how to do this

A "solution" to this pair of equations is a pair of numbers, for 'a' and 'b',
that make the equations true statements.

I can tell you right now that this system of equations has no solution.
Here, let me show you why:

           4a = 4 - b
           4a = 5 - b

Subtract the bottom equation from the top one:

             0 = -1

Can you think of any numbers for 'a' and 'b' that could
make  0  equal to  -1 ?

I can't either.

There are no numbers for 'a' and 'b' that can make both equations true
statements.  That's just another way to say that the system of equations
has no solution.