To write 0.8918 as a fraction you have to write 0.8918 as numerator and put 1 as the denominator. Now you multiply numerator and denominator by 10 as long as you get in numerator the whole number.
0.8918 = 0.8918/1 = 8.918/10 = 89.18/100 = 891.8/1000 = 8918/10000
as simplified it would be 4459/500