Answer #62. also, can you tell me what's the mathematical sentence for #62?

The operations you would use are multiplication and subrtraction
(the reason for this is because you need to find the cost for 30 people normally   --12*30 -- and then subtract the discount -- 3*30 -- to find the total cost)

In the mathematical sentence (also known as the equation) we'll let the variable 'c' equal the total cost for all 30 students.

This means c=12(30) -3(30)
To break it down you write it this way because you need to find the cost before the discount (12*30), then subtract the discount (3*30) to get the total cost (c). 

Next, you just need to solve; 
c=12(30)-3(30)
c=360-90
c=270

This means that the total cost for all 30 students will be $270. 

I hope this helps!!!