QUES: By adding these two costs together we can derive the total cost

correct the punctuation.

CORRECTED: By adding these two costs together, we can derive the total cost.

QUES: In the early morning it will be still overcast but mainly dry After late morning clouds with local rain will dominate

correct the punctuation.

CORRECTED: In the early morning it will be still overcast, but mainly dry. After late morning clouds with local rain will dominate.

QUES: The beautiful building houses exhibition galleries mosaic floors walls painted in fabulous colours columns and a maze of corridors and rooms

correct the punctuation.

CORRECTED:
The beautiful building houses exhibition galleries, mosaic floors, walls painted in fabulous colours, columns and a maze of corridors and rooms.