Mock exam – throughput q

Throughput Q:

Co makes 2 products: X and Y.
X Y
SP 50 32
Material 10 6
Labour 20 15
Assembly time 20min 15min
Max demand 1500 units 1000units

Total assembly time is limited to 600hrs. Using throughput, how many units Y should produce?

First contribution:

X: 50-10=40/0.3hrs=133.3, so X FIRST
Y: 32-6=26/0.25hrs=104, Y SECOND

X: 1500u*0.3=450hrs
Y: 600u*0.25=150hrs

Where am I getting wrong, as my answer of 600units does not match any of the mock exam?