why the formula is not being copied to the bottom cells

see the attached file. the total is on H3. when i drag the total to downwards i do not get the correct result.on H3 it is supposed to be the total of D3:G3. but from D4:G4,it not like that. so the error.

when i drag the total to downward from H3, I get 58 in all the cells which is wrong. now i would like to know why this happens and how can edit it to get the correct result from H4 downwards.

i have copied and pasted the values from another sheet. thanks