請幫忙數學列式

1) A and B started at the same time from two towns 162 km apart. They met in 6 hours. If A's speed was 12 km per hour, what was B's speed?
Let v km/h be the speed of B,
12(6) + b(6) = 162

2) Two cars are 600 km apart . One car's speed is twice the other. If they pass each other after 10 hours, find their speeds.
Let v km/h be the speed of one car,2v km/h be the speed of the other car
v(10) + 2v(10) = 600

3) Tina is six years older than her sister. In two years she will be twice as old as her sister. Find their present ages.
Let t be the present age of Tina,then,her sister is t - 6,
t + 2 = 2((t - 6) + 2)