Solve by substitution and solve by graphing

Solve by Substitution:
2x+4y = 30
y=3x+4

Solve by graphing:
y= x-4
3x+y=8



How do you do these math problems? Please explain.

2x+4y=30-----------------------(1)
y=3x+4------------------------------(2)
substitute y from (2) to (1)
2x+4(3x+4)=30 replace y = 3x+4
2x+12x+16=30
14x+16=30
14x=30-16 subtract 16 both sides
14x=14
x=14/14 divide by 14
x = 1
substitute x=1 in (2)
y=3.1+4
y=7
for the graphing problem you can use a calculator. Graph this two equation and see where two line intersect that point is your solution

2x + 4(3x+4)= 30
2x + 12x +16 = 30
14x =14
x=1

y = 3(1)+4
y-7

sorry i don't get ms joy's class anyway