Question

how to do this? 3x-4y=-1 and x+y=5 in substitution

Answer 1

haha. okay, so apparently the first answer wasn't good. you need to solve one of your equations for one of the variables. for example, solving the second equation for "y" gives
y = 5 - x

Answer 2

this can be substituted. to make this easier, put the right hand side of your solved equation directly into the left, using parentheses, like this:
3x - 4(5-x)=-1

Answer 3

okey.okey okey yes i forgot .tnx

Answer 4

y = 5 -x

3x - 4y = -1
3x - 4(5-x) = -1 (see azeotrope's explanation)
3x -20 + 4x = -1 distribute -4 to the terms inside the parenthesis
7x -20 = -1 combine similar terms
7x = -1 + 20 transpose -20 to the other side
7x = 19 do the operation
x = 19/7 divide both sides by 7