A determined 90-year-old has vowed to scale the equivalent of a mountain on the stairs of her Highland home to repay the NHS for the care it gave her late husband.Margaret Payne, a great-grandmother-of-four from the remote village of Drumbeg in Sutherland, says she will climb 2398ft - the height of nearby Suilven - by tackling the 17 stairs in her house hundreds of times.Despite having had two knee replacements, the former fish farmer told the Record she was inspired to take on the challenge after seeing veteran Tom Moore, 99, raise £10million for the NHS by walking laps in his Bedfordshire garden.She said: “I’ve had knee trouble since I was 12.