I have Type-declaration character does not match declared data type error in O = C * (H^(1.5)) about H

Sub routing()
Dim A, B, C, DT, DH, HT, E, F, G, H, S, O As Double
Dim i, j, K, N As Integer
C = Cells(3, 6).Value 'ZARIB DEBI'
A = Cells(4, 6).Value 'MASHATE AVALIYE'
B = Cells(5, 6).Value 'AFZAYESHE MASAHAT'
DT = Cells(6, 6).Value 'DELTAT'
HT = Cells(7, 6).Value 'KOLE ERTEFAE DARN NAZA GEREFE SHODE'
DH = Cells(8, 6).Value 'DELTAH'


N = HT / DH
For i = 1 To N
H = i * DH
Cells(2 + i, 10).Value = H
O = C * (H^(1.5))
Cells(2 + i, 11).Value = O
S = 1000000 * (A * H + 0.5 * B * (H^(2)))
Cells(2 + i, 12).Value = S
G = S / DT + O / 2
Cells(2 + i, 13).Value = G


Next i
End Sub