Find the values of x and y for the isosceles trapezoid

If the trapezoid is isosceles, angles A and C are supplementary, so ...

... (4x+4) +(7x+11) = 180

... 11x +15 = 180 . . . . . . collect terms

... 11x = 165 . . . . . . . . . subtract 15

... x = 15 . . . . . . . . . . . . divide by the coefficient of x

And angles C and E are congruent.

... 4·15 +4 = 21y +1

... 63 = 21y . . . . . subtract 1

... 3 = y . . . . . . . . divide by the coefficient of y

6mm^3 or .6cm^3

      216

      /   \

  36     6

  /   \     /

6     6   6

factor trees are nice.