The circumcenter is where the perpendicular bisectors meet.
if you sketch the triangle, you will see that it is a right triangle, with the right angle vertex at (2,1)
one perpendicular bisector is x=1, another perpendicular bisector is y=3
they meet at (1,3)
so (1,3) is the answer.
Sets of three integers that could be right triangles are called pythagorean triples. the only pythagorean triple including 7 is 7, 24, and 25. so the length of the other leg is 24 and the length of the hypotenuse is 25. hope this helped!
To solve an equation or inequality, you can add the same value to both sides of the expression. Here, it is convenient to choose that value to be the opposite of the constant (+15) added to y, so that constant is replaced by zero.
y + 15 - 15 < 3 - 15 . . . . . we have added -15 to both sides
y < -12 . . . . . . . . . . . . . . . the result of simplifying. This is your solution.