Without knowing the relationship between h and x, how is this possible?
x / r = [ x + h ] / R
x (R / r ) = x + h
x (R/r) - x = h
x [( R/r) - 1 ] = h
x = h / [ (R/r) - 1 ]
H = x + h
H = h / [ (R/r) -1 ] + h