plugging the coordinates into the equation of the circle, we observe that the equation is true since both sides of the equation are equal(value on both sides of the equal sign are same). This wouldn't be true if for instance the left side of the equation evaluated to ≠100. Therefore we can conclude that the rose bush lies on circle since the equation is true
One inch of board is left if you subtract the two 3 inches pieces from the board the further subtract the 24 inches from the three 8 inches pieces you get 31-30