Answer:
1) 620/33
2)2141/495

Step-by-step explanation:

1)18.78

Let us take x= 18.78 ( The underline represents the bar over the number )
x=18.78

100x=1878.78

100x-x=1878.78-18.78

99x=1860

x=1860/99
Simplified: 620/33

2) 4.325
Let us take x= 4.325
x=4.325
10x=43.25
1000x=4325.25
1000x-10x=4325.25-43.25
990x=4282
x=4282/990
Simplified: 2141/495