Use pythagorean Theorem which is a^2 + b^2 = c^2 where a and b are the sides of the triangle and c is the hypotenuse, in other words the longest side.
Since x is in line with the center of the circle and is perpendicular with line that measures 15.6 cm we know that one side of the triangle is half of 15.6 or 7.8.
So then we input our known values into the formula and solve for the missing one. The formula looks like this
