Simultaneous Equations

Question 1

Substitution Method

Answer 1

Substitute one equation for one of the variables in the other equation.
Eg. y=7-2x             y=7-2(3)
      3y+9x=30       y=7-6
3(7-2x)+9x=30    y=1
21-6x+9x=30
3x=30-21
x=9/3
x=3

Question 2

Elimination Method

Answer 2

Same sign add

Different sign subtract