Answer:
48. option C : Substitution
49. Option D : ( 3, 6)
Explanation:
3x + y = 15 ------------- ( 1 )
y = 2x ------------------- ( 2 )
Substitute ( 2 ) in ( 1 ) :
3x + y = 15
3x + 2x = 15
5x = 15
Substitute x in ( 2 ) :
y = 2x
y = 2 × 3 = 6
The solution to the system of equation is ( 3 , 6 )