**Let the speed = x km/h. Distance = 360km**

**then time taken = distance/speed**

t1=360/x

if speed is increased by 5 km/h

speed will be (x+5)km/h and distance is the same

t2= 360/(x+5)

time with original speed - time with increased speed = 1

**i.e. t1 -t2 = 1**

360/x - 360/(x+5)=1

LCM= x(x+5)

(360(x+5)-360x) /x(x+5)=1

360x+1800-360x=x(x+5)

x^{2}+5x = 1800

x^{2}+5x-1800=0

x^{2}+45x-40x-1800=0

x(x+45)-40(x+45)=0

(x-40)(x+45)=0

x= 40 km/h will be the original speed. (since, speed can't be negative and hence, can't be equal to -45km/h)