Solve the following pair of (simultaneous) equations using method of elimination by substitution :

2x - 3y + 6 = 0

2x + 3y - 18 = 0

Find the value of m, if x = 2, y = 1 is a solution of the equation 2x + 3y = m.

Solve :

10% of x + 20% of y = 24, 3x - y = 20