How would convert 1450000mg to scientific notation and what's the answer !

1450000mg is 1.45mg x 10^6

The decimal point in 1450000 would be after the last zero so you move that decimal point until it reaches before the last number which is 1 so that gives you 1.45. Count how many times you moved from the original decimal position to the decimal point after 1. The number of times you moved will be your exponent. If you want to check if your answer is right, then move the decimal point of 1.45 to the right by the number of your exponent.