Use the Pythagorean theorem for triangle ABD to find the hypotenuse.
7.5^2+4.9^2=c^2. After solving you get that the missing length is about 9 cm. The hypotenuse of ABD is also a leg for ABC so you can use a trigonometric function, tangent, to find x. Set up the equation for opposite and adjacent sides to angle measure 55.8. The equation is tan(55.8)=9/x. In order to isolate the variable you multiply both sides by x to get (x)tan(55.8)=9, then divide both sides by tan(55.8), this leaves you with x=9/tan(55.8). You can then plug this into the calculator to get x is approximately 6.1 cm.
