[NeoN]

мой вариант просто так)

var arr = [];
arr [0] = "1 + 2 =3";
arr [1] = "3* 2 =6";
arr [2] = "2+5 =7";
arr [3] = "1 +2=3";


function compareBySecond(a,b){
	let number = n => Number(n.match(/(\d+)\s*\=\d+$/)[1]); 
	return number(a) - number(b);
}

function compareByAnswer(a,b){
	let number = n => Number(n.match(/(\d+)$/)[1]); 
	return number(a) - number(b);
}

arr.sort(compareBySecond);
alert(arr);

arr.sort(compareByAnswer);
alert(arr);