Which property is demonstrated below? (4*3)*7=4*(3*7)

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.

The? half-life of a radioactive substance is 20 years. if you start with some amount of this? substance, what fraction will remain in 120 ? years

Lines a and b are perpendicular. if the slope of line a is 3, what is the slope of line b?