Notice: Undefined variable: b in D:\env\php\inc\hdr.php on line 2

Notice: Undefined variable: b in D:\env\php\inc\hdr.php on line 4

Notice: Undefined variable: b in D:\env\php\inc\hdr.php on line 6

Notice: Undefined variable: a in D:\env\php\inc\hdr.php on line 13

Fatal error: Uncaught Error: Function name must be a string in D:\env\php\inc\hdr.php:13 Stack trace: #0 {main} thrown in D:\env\php\inc\hdr.php on line 13