Solve the system of two equations using subsitution or elmin

Solve the system of two equations using subsitution or elmination?

7x + 5y + 3z =144 and x + y + z=30

with 2 equations and 3 variables we cannot have single set of solution

given

7x + 5y + 3z =144 ----------------->(1)

x + y + z=30------------------->(2)

multiply (2) with 3

3x +3y +3z =90------------->(3)

subtract (3) from (1)

7x + 5y + 3z -3x -3y -3z =144-90

4x +2y =54

2(2x+y)=54

2x+y=27

x=(27-y)/2

so lution is

z =t

y =s

x =(27-s)/2