Systems of two linear equations in two variables SAT question

The correct answer is $\frac{9}{5}$. Multiplying the first equation in the given system by $2$ yields $10x+28y=90$. Subtracting the second equation in the given system, $10x+7y=27$, from $10x+28y=90$ yields $(10x+28y)-(10x+7y)=90-27$, which is equivalent to $10x+28y-10x-7y=63$, or $21y=63$. Dividing both sides of this equation by $21$ yields $y=3$. The value of $x$ can be found by substituting $3$ for $y$ in either of the two given equations. Substituting $3$ for $y$ in the equation $10x+7y=27$ yields $10x+7(3)=27$, or $10x+21=27$. Subtracting $21$ from both sides of this equation yields $10x=6$. Dividing both sides of this equation by $10$ yields $x=\frac{6}{10}$, or $x=\frac{3}{5}$. Therefore, the value of $xy$ is $(\frac{3}{5})(3)$, or $\frac{9}{5}$. Note that 9/5 and 1.8 are examples of ways to enter a correct answer.