If I have 7 pencils and my friend gives me 3 pencils, how many pencils do I have total?

7 pencils + 3 pencils = 10 pencils

If the velocity of an object at any particular given time=t seconds is 7t^2+7 m/s, what is the velocity and acceleration of the object at t=3?

velocity = 7t^2 + 7, thus veloctity at t=3 is equal to 70m/s Since acceleration is the derivative of velocity f'(t) = 14t thus f'(3) is 52m/s^2

Emily had $24 to spend on seven pencils. After buying them she had $10. How much did each pencil cost?

If Emily had $24 to start and ends up with $10 the difference is $14, meaning she spent $14 dollars on pencils. If she bought seven pencils this means $14/7 = $2 per pencil