The exponent 3/7 means raise everything to the 3 'power' and then take the '7th' root....
....so first choice is no good (cube root or 3rd root)
5^3 = 125 so the 3rd choice looks good
(x^3)^3 = x^9 so the third choice still looks good
(y^4)^3 = y^12 so the third choice it is!