Property 'forkJoin' does not exist on type 'typeof Observable'. code example

Example 1: Property 'of' does not exist on type 'typeof Observable'.

import { of } from 'rxjs';

Example 2: Property 'fromPromise' does not exist on type 'typeof Observable'. rxjs 6

import { from } from 'rxjs';

var observableFromPromise =  from(promiseSrc);