So to do the math properly you have to convert the 7.20 into a fraction as well so the 7$ will be a while number and the .20 would be over 100 being 20/100 since there’s 100cents in 1$, so that would be 7 20/100 and since the pounds is 3 3/5 the denominators have to be the same so you’ll have to divide the 20/100 until you have a same denominator so if you dive the numerator and denominator by 5 you get 4/20 (20/5=4, 100/5=20) then again you divide them both by 4 being 1/5 so that would be 7 1/5 x 3 1/5 so for each of them you multiply the bottom and add the top so 7x5 = 35+1= 36 so that’s your new numerator but the denominator remains the same so 36/5 and you do the same with 3 3/5 you multiply 3x5=15+ the 3 = 18/5 so then that would be 36/5 x 18/5 now you multiply both the numerators and denominators equaling 648/25 then that equals to 25.92$