Speedometer and Odometer not reading, bad fuel consumption

I have a 1995 model Toyota RAV4 automatic transmission. The speedometer and Odometer sometimes works, sometimes doesn’t. What could be the problem causing this erratic behaviour.

The same car consumes much fuel per kilometer (1 liter for 7 Kilometers). What could be the problem behind this terrible fuel consumption?

Also when changing gear to reverse there is a there is knocking sound.

May i have answers for for these problems please.

Dare-es-Salaam, Tanzania