Which regular polygon will tessellate alone?

a. triangle
b. pentagon
c. heptagon
d. decagon

When are two distinct non vertical lines parallel

Quick translate "x is 12 units from 20" into an equation. what are the values of x being described? if you can answer any of my other questions that'd be great too

y=2x−1 5x−4y=1 is (1,1)(1,1) a solution of the system?