I am building my robot, and I need to know how to find out the mechanical advantage of two powered 60 teeth sprockets, then one 10 teeth sprocket.
I’m not sure if that the amount of teeth I wrote are what vex sells, but it’s just to make it easier. 
Alright. The way this works is that you have to figure out the gear ratio and from there you can figure out what kind of torque and speed you will end up with.
To use your scenario: you have a 60 tooth sprocket attached to the motor which is then driving a 10 tooth sprocket attached to, say a wheel. For every 1 turn of the motor the 10 tooth sprocket and the wheel it is attached to will spin 6 times. Therefore you have a 1-6 gear ration (number of turns of the motor-number of turns of the driven gear or sprocket). From this we can figure out that if the motor is turning at 100 rpm (rotations per minute) then the 10 tooth sprocket would spin 600 times per minute (600rpm). You must also account for the torque. Now if you are gaining speed in a gear ration you are giving up some torque. In this case the final torque output on the shaft the 10 tooth gear is on will only be 1/6th the torque the motor is putting out.
If the sprockets were reversed (10 tooth on the motor and it is driving the 60 tooth) you would have a 6-1 ratio. This type of gearing is used to gain torque but it gives up speed. In this case (assuming motor speed of 100rpm) the final output speed would be 100rpm/6 or about 17rpm however the torque would be 6 times the torque that the motor is putting out.
Hope that helps
~DK
Awesome! thank you so much.