math

(.200+x)(.200)/[(.500)(.500)] = 6.25

Note....  .200  = 1/5,  .500  = 1/2     and   6.25  = 6 + 1/4  =  25/4   ......so we have

( 1/5 + x) (1/5) / [ 1/2 * 1/2 ]  = 25/4

[ 1/25 + (1/5)x  ]  /  ( 1/4)   =  25/4        multiply both sides by 1/4

1/25  +  (1/5)x    =    25/16        

Multiply through by the common denominator, 400

16   + 80x    =   625       subtract 16 from both sides 

80x   =  609      divide both sides by 80

x  =  609 / 80  = 7.6125