What is this line called on a ruler and what is it used for? P. S. If you don't know is don't answer please :)

Which shows the correct substitution of the values a,b and c from the equation 1=-2x+3x^2+1

The areas of two similar triangles are 72dm2 and 50dm2. the sum of their perimeters is 226dm. what is the perimeter of each of these triangles?

Point r divides in the ratio 1 : 5. if the coordinates of e and f are (4, 8) and (11, 4), respectively, what are the coordinates of r to two decimal places?