D) 9x=18
Explanation
given
[tex]\begin{gathered} y=3x\Rightarrow equation(1) \\ 3x+2y=18\Rightarrow equation(2) \end{gathered}[/tex]
Step 1
substitute the y value from equation (1) into equation(2)
so
[tex]\begin{gathered} 3x+2y=18\operatorname{\Rightarrow}equat\imaginaryI on(2) \\ replace \\ 3x+2(3x)=18 \\ 3x+6x=18 \\ add\text{ like terms } \\ 9x=18 \end{gathered}[/tex]
therefore, the answer is
D) 9x=18
I hope this helps you
