so I just need some help understanding a solution that my teacher has given

the question being when will a police cruiser pass a speeding car and in the solution, they showed this

Dp(police) =Ds(speeder)
200m +(40m/s)T= 300 m + (30m/s)T
10m/sT=100m
t=10

my question being why is their T on only 1 side?

they collected all the T terms on the left

40T-30T = 10T