Hello! So you will use the Pythagorean Theron equation which is Asquare + bsquare=C square Plug in what you are given to find the missing piece
A square+ (2.6)square= (6.2) square Asquare+ 6.76= 38.44 (Subtract 6.76to both sides to isolate A) Asquare= 31.68 (Take the square root of both sides to find out what A is) A=5.628