solutions for codewars challenges in javascript

solutions.js

//Rearange Number to Get its Maximum
var maxRedigit = function(num) {
var ou=[];
var snum=num.toString();
if (num<=0 || snum.length!=3){return null}
for (var i=0,len=snum.length;i<len;i+=1){
	ou.push(+snum.charAt(i));}
var a=ou.sort(function(a,b){return b-a}).join('');
return parseInt(a)
};
//Sir , showMe yourID
function showMe(yourID){
var s=yourID.match(/^[0-9-a-z-]|-[a-z]|-$|\s/)
if (s==null){return true;}else{return false;}
}
//The Coupon Code
function checkCoupon(enteredCode, correctCode, currentDate, expirationDate){
var curdate=new Date(currentDate);
var exdate=new Date(expirationDate);
  if(enteredCode!==correctCode || curdate>exdate){return false}else{return true}
}
//Name on billboard
function billboard(name, price = 30){
var a=name.length;
var tot=0;
for(i=1;i<=a;i++){
tot+=price;
}
return tot
} 

//How old will I be in 2099?
function  calculateAge(p,r) {
  if (r-p>1){
return "You are "+(r-p)+" years old."
}else if(r===p-1){
return "You will be born in "+(p-r)+" year."
}else if(r<p){
return "You will be born in "+(p-r)+" years."
}else if(p===r-1){
return "You are "+(r-p)+" year old."
}else{
return "You were born this very year!"
}

}
//Fix your code before the garden dies!
function rainAmount(mm){
    if (mm < 40) {
         return "You need to give your plant " + Math.abs(40-mm) + "mm of water"
    }else {
         return "Your plant has had more than enough water for today!"
    };
}
//Sum of positive
function positiveSum(arr) {
var sum=0
for(i=0;i<arr.length;i++){
if (arr[i]>=0){sum=sum+arr[i]}
}
return sum  
}
//Heads and Legs
function animals(heads, legs){

var x=(4*heads-legs)/2;
var y=heads-x;
if (x<0 || y<0){return 'No solutions'}
if (x===Math.round(Math.abs(x))){return [x,heads-x]}else{return 'No solutions'}
}
//Match My Husband
function match(usefulness,months){
    var sum=usefulness.reduce(function(a,b){return a+b;},0);
    var grvt=100*Math.pow(Math.E,-0.15*months);
    if (sum>=Math.round(grvt,3)){return 'Match!';}else{return 'No match!';}
   
}