Given an array of math equations (given as strings), return the percentage of correct answers as a string. Round to the nearest whole number.
markMaths(["2+2=4", "3+2=5", "10-3=3", "5+5=10"]) ➞ "75%"
markMaths(["1-2=-2"]), "0%"
markMaths(["2+3=5", "4+4=9", "3-1=2"]) ➞ "67%"