SHOW WORK I’ll mark you brainlist

Evaluate the expression for the given value of the variable 7a - 4a for a =8

Varies inversely with x. if y=8.5 when x=-1 find x when y=-1

Astrid spent $36 on new shoes. this was $12 less than twice what she spent on a new skirt. part a: which equation would solve for how much she spent on the skirt? part b: solve the equation in the workspace provided below. how much did astrid spend on her skirt?