Does anyone know how to do Elimination and work it out?

Let's label your equations:
0.05x+0.15y=25...............(i)
0.10x+0.05y=25..............(ii)

To solve by elimination either the terms in x or in y must be equal, so let's multiply equation (i) by 2 and them subtract equation (ii) from (i):

(i) x 2 .......... 0.10x+0.30y=50
(ii)................. 0.10x+0.05y=25

(i) - (ii): ....... 0+0.25y=25
-> 0.25y=25..........(iii)
(iii)/0.25: y =100

substitute 100 for y in (ii):
0.10x+0.05(100)=25
-> 0.10x+5=25
-> 0.10x=25-5
-> 0.10x=20
-> x=200