Question 922344
5x=(5+4)*45
x=9*9
x=81 kph to catch it in 5 hours

another way

The first car had  a head start of 180 (4*45) km
the second car needs to gain 
180/5=36 km 
so it must travel at 
45+36=81 kph



check
Gaining speed 81-45= 36 mph
Head start 45*4 =180 miles
Time to catch up 180/36=5 hours
Algebraic solution
45(t+4)=81t
45t+180=81t
180=81t-45t
180=36t
t=5 hours
Distance to meeting 5*81=405 miles