Group variable terms together:
First the y's: (0.7-0.2)y=0.5y,
Then the r's: (2.1+2)r=4.1r,
Then the constants: -2100+140=-1960.
So the equation becomes 0.5y+4.1r-1960=0 which can be arranged in different ways, e.g., y=3920-8.2r.
There's only one equation so there are many solutions for y and r, but the equation shows the relationship between y and r which can be graphed: