Algebra question/geometry solving the system 3x + 2y = 21, (7 - x)² + y² = 2².
what does this mean ?
How to get the answer  (7−4/√13,6/√13)

This means that you have a linear graph 3x+2y=21 and a circle, with origin at (7,0) and a radius of 2. To solve this system, you need to find the intersection point of these 2 graphs. 
Edit:
My algebraic solution:
$3x+2y=21\\
2y=21-3x\\
y=\frac{21-3x}{2}\\
(7-x)^2+\frac{9}{4} \cdot (7-x)^2=4\\
\frac{13}{4} \cdot (7-x)^2=4\\
(7-x)^2=\frac{16}{13}\\
x-7=\pm \frac{4}{\sqrt{13}}\\
x=7 \pm \frac{4}{\sqrt{13}}$
