Presumably we're being asked to solve the system.
4x - 7y = 15
5x - 2y = 12
We don't really have any common factors among the coefficients of x, or among the coefficients of y, so we can do the general thing. To eliminate y multiply the first equation by (typically the absolute value of) the coefficient of y in the second equation and vice verse, then add or subtract equations to eliminate.
First equation times 2:
8x - 14y = 30
Second equation times 7:
35x - 14y = 84
Subtract,
27x = 54
x = 54/27 = 2
2y = 5x - 12 = 10 - 12 = -2
y = -1
Answer: x=2, y = -1
Check:
4(2)-7(-1)=8+7=15, good
5(2) -2(-1) = 10 + 2 = 12, good
-----
If you do enough of these 2x2 linear systems you can learn to just write down the answer. I usually remember the matrix inverse, but if you haven't gotten there you can just remember the pattern:
ax + by = c
dx + ey = f
has solutions
x = (ce-bf)/(ae-bd), y = (a f-cd)/(ae-bd)
4x - 7y = 15
5x - 2y = 12
has solutions
denom = ae-bd = 4(-2) - (-7)(5) = 27
x = (15(-2) - (-7)(12))/27 = (-30 + 84)/27 = 2
y = (4(12)-15(5))/27 = (48-75)/27 = -27/27 = -1
