A level mechanics question

I don’t quite know how to work our part b to this question, please could I have some help?

A particle P passes through point A with velocity 2.8ms-1 and constant acceleration 0.12 ms-2. Three seconds later a second particle Q passes through A with velocity 2.4ms-1 and constant acceleration 0.2ms-2.

a) Write down expressions for the displacement of P and Q from A, in terms of t, where t seconds is the time after P passed through A.

b) Show that when the particles meet, 2t* – 50t - 315 = 0

My current workings:

P:
S=?
U=2.8
V=?
A=0.12
T=t

Q:
S=?
U=2.4
V=?
A=0.2
T=t-3

S=UT+1/2AT*
P: S=2.8t + 0.6t*
Q: S=0.1t* + 1.8t + 0.9

I don’t quite know how to work our part b to this question, please could I have some help?

A particle P passes through point A with velocity 2.8ms-1 and constant acceleration 0.12 ms-2. Three seconds later a second particle Q passes through A with velocity 2.4ms-1 and constant acceleration 0.2ms-2.

a) Write down expressions for the displacement of P and Q from A, in terms of t, where t seconds is the time after P passed through A.

b) Show that when the particles meet, 2t* – 50t - 315 = 0

My current workings:

P:
S=?
U=2.8
V=?
A=0.12
T=t

Q:
S=?
U=2.4
V=?
A=0.2
T=t-3

S=UT+1/2AT*
P: S=2.8t + 0.6t*
Q: S=0.1t* + 1.8t + 0.9