Area is length times width [A=(L)(W)], if we know that the area of the card is 3/10 and the length is 4/5 we can set up the equation 3/10=(4/5)(W) where W is width. Solve for W by deciding both sides by 4/5 and we get that W=3/8. To find the perimeter of the card were have to add up all the sides of the card so 3/8+3/8+4/5+4/5 which equals 47/20