400 million as a standard form and it isn't 400,000,000

Of the ones listed here, the factor that had the greatest impact on the eventual destruction of native americans' ways of life was the development of the a) automobile. b) highway. c) railroad. d) steamboat.

For each proportion find the unknown number x 1/5/8=×/15

The amount spent on food and drink by 20 customers is shown below what is the modal amount spent ?