Short answers, pulled from the story.
Viking 1 landed on Mars on the 20th of July 1976, and Viking 2 soft-landed on the 3rd of September 1976. Both landers were launched in 1975 aboard Titan IIIE rockets and reached Mars orbit in the summer of 1976.
NASA spent roughly one billion dollars in 1970s money on the Viking program. The most expensive single component was the lander's life-detection unit, which cost about 60 million dollars at the time of the mission.
One Viking biological experiment returned a positive signal for metabolism, but two other experiments found no organic molecules in the soil, and most scientists attributed the positive result to non-biological chemistry. The question remains unresolved; a 2008 discovery by the Phoenix lander of perchlorate salts in Martian soil introduced new uncertainty into the original Viking results.
The Viking 1 lander operated the longest, for 6 years, 3 months, and 22 days, before a software update error caused its antenna to lose contact on the 13th of November 1982. The Viking program was officially ended on the 21st of May 1983.
Viking orbiter images revealed huge river valleys, branched stream networks in the southern hemisphere, and impact craters whose ejecta had flowed like mud, all indicating that large amounts of liquid water once existed on Mars. The estimated volume of water that carved some channels was ten thousand times the flow of the Mississippi River.
Thomas A. Mutch, a geologist at Brown University in Providence, Rhode Island, led the Viking lander imaging team. The camera system cost 27.3 million dollars to develop, and finding a manufacturer capable of building the advanced design proved difficult.