Solve the simultaneous equations: 5x + y = 21 x - 3y = 9

To solve this you should solve by substitution, as the there are singular values of x and y in one of two equations. Lets first label the equations as 1) and 2).1) 5x + y = 212) x - 3y = 9Lets make x the subject of 2), and substitute x into equation 1.x - 3y = 9 becomes x = 9 + 3y, as you add '3y' to both sides of the equation.Substituting x = 9 + 3y into 1), gives you 5(9 + 3y) + y = 21. (Remember to keep the substitution of x in brackets - it's its own value!)Expand the brackets (follow BIDMAS - brackets, indices, division, multiplication, addition, subtraction)Equation 1) now becomes 45 + 15y + y = 21, collect the like terms to give you 45 + 16y = 21.I like to tidy up my equations, to make the 'unknown' value(s) the start of the equations: 16y + 45 = 21Rearrange and solve.16y = 21 - 45 (subtract 45 on both sides)16y = -248y = -12 (divide by 2 on each side to simplify)4y = -62y = -3y = -3/2 (divide by the integer holding y, in this case 2)y = -1.5 (leave as fraction or decimal)Now to substitute our found value y into the equation of x, to find x.x = 9 + 3yx = 9 + 3(-1.5)x = 9 - 4.5x = 4.5Therefore,x = 4.5, y = -1.5