Given equations a and b as 2/5x+y=12 and 5/2y-x=6 , respectively, which expression will eliminate the variable x?

lets work with the equations system:
(2/5)x + y = 12
(5/2)y - x = 6
first lets eliminate the fractions multiplying by a suitable number, 5 and 2, each equation:
2x + 5y = 60
5y - 2x = 12
rearrange and add the equations:
 2x + 5y = 60
-2x + 5y = 12

0 + 10y = 72
10y = 72
now we have eliminated the x variable and can solve the system