Write the number in standard notation. 6.43x10^4

Which is f(5) for the function –2x2 + 2x - 3?

Abicycle training wheel has a radius of 3 inches. the bicycle wheel has a radius of 10 inches.approximately how much smaller, in square inches and rounded to the nearest hundredth, is the area of the training wheel than the area of the regular wheel? *

The difference of two numbers is 40. find the numbers if 0.3 parts of one number is equal to 37.5% of the other one.