Multiply the second equation by -3: -3.9x+2.7y=-17.1 and add to the first equation:
(0.7-3.9)x=7.5-17.1=-9.6.
-3.2x=-9.6 which is the same as 3.2x=9.6 and x=9.6/3.2=3.
Knowing x=3 we can plug this into either equation to find y:
2.1-2.7y=7.5, 2.7y=2.1-7.5=-5.4, making y=-5.4/2.7=-2.
So the solution is x=3, y=-2.