The diameter of a circle is 14 cm find it’s circumference in terms of pie

Will give brainliest sum of arithmetic series (sigma notation) find the numerical answer to the summation given below. (image shown below)

Solve each quadratic equation by factoring and using the zero product property. [tex]x^2+6x+8=0[/tex]

Atrain leaves little? rock, arkansas, and travels north at 90 kilometers per hour. another train leaves at the same time and travels south at 80 kilometers per hour. how long will it take before they are 680 kilometers? apart?