function asyncAddOne(x, callBack) {
  setTimeout(function() {
    return callBack(x + 1);
  }, 200);
}

function asyncDouble(x, callBack) {
  setTimeout(function() {
    return callBack(x * 2);
  }, 200);
}

function asyncTimesTen(x, callBack) {
  setTimeout(function() {
    return callBack(x * 10);
  }, 200);
}

// Create this function!
function waterfall(arg, tasks, cb) {
  let count = 0;
  let x = arg;
  if(count < tasks.length) {

    tasks[count](x, function (x) {
      count++;
      tasks[count] (x, function(x) {
        count++;
        tasks[count] (x, function(x) {
          count++;
          cb(x);
        });
      });
    });
  };
}

waterfall(3, [asyncAddOne, asyncDouble, asyncTimesTen], function(result) {
  console.log('Test 1');
  if (result !== 80) {
    console.log('test failed, expected 80 but got', result);
  } else {
    console.log('Test 1 passed!');
  }
});