A car covers 15 km, 20 km, 30 km and 12 km at speeds of 20 km/h, 30 km/h, 40 km/h and 30 km/h,respectively. The average speed of the car for the total journey is :

Time taken by the car to cover 15 km distance at speed of 20 km/h = $$\frac{15}{20}$$ h

Time taken by the car to cover 20 km distance at speed of 30 km/h = $$\frac{20}{30}$$ h

Time taken by the car to cover 30 km distance at speed of 40 km/h = $$\frac{30}{40}$$ h

Time taken by the car to cover 12 km distance at speed of 30 km/h = $$\frac{12}{30}$$ h

Total Time = $$\frac{15}{20}+\frac{20}{30}+\frac{30}{40}+\frac{12}{30}$$ = $$\frac{90+80+90+48}{120}$$ = $$\frac{308}{120}$$ = $$\frac{77}{30}$$ h

$$\therefore\ $$Average speed of the car for the total journey = $$\frac{\text{Total distance}}{\text{Total Time}}$$ = $$\frac{15+20+3+12}{\frac{77}{30}}$$ = $$\frac{77\times30}{77}$$ = $$30$$ km/h

Hence, the correct answer is Option C