An astronaut has a mass of 70 kg on earth. What would her mass be in mars? What would her weight be on mars?

Mass remains the same!

And about the weight,

Gravitational force on Earth is around 9.8 m/s^2

Gravitational force on Mars is around 3.7 m/s^2

3.7/9.8 = 0.377

So, the astronaut will weight around = 70 * 0.377 = 26.39N

So, the answer is 26.39N