$37$ Pens and $53$ pencils together cost Rs. $320$ while $53$ Pens and $37$ Pencils together cost Rs. $400$, Find the cost of a Pen and that of a Pencil.
So far I had done the following: Let cost of 1 Pen be $\mathrm{Rs}.x$
And let cost of $1$ Pencil be $\mathrm{Rs.}y$
So, equations will be:
$37 \cdot x + 53\cdot y = 320 \mathrm{-----} (1)$
$53 \cdot x + 37 \cdot y = 400 \mathrm{-----} (2)$
Now which formula I should apply to solve this linear equation in two variables.
Please Help