i don't get this whole concept what-so-ever so lets start with problem one y= -3X +5
5 X - 4y = -3
Your first equation tells a value for Y. Substitute that in the second equation.
5x - 4(-3x + 5) = -3
5x + 12x - 20 = -3
17x = 20 - 3
17x = 17
x = 1
Now substitute 1 for x in the first equation to find a value for y.