-7(-4f-1)=28f+7 the number outside parentheses is multiplied by everything inside (distributive law). Minus time minus makes plus.
[-7-(4f-1)=-7-4f+1=-6-4f looks similar, but the parenthesis has moved slightly. This time the minus is applied to everything inside so it changes -1 into +1, and 4f into -4f. -7+1=-6.]