A pre-paid plan charges: R1 per minute for calls and R0.50 per mb of data. (A) If you talk for 9 minutes and use 2mb of data, write an expression for the total cost. (B) What will be the total cost if you talk 30 minutes and use 20mb of data?

Here's the solution for the prepaid phone charges:

Step 1: Identify the given rates.
Cost per minute for calls = K1
Cost per MB for data = K0.50

a) If you talk for g minutes and use mb of data, write an expression for the total cost.
The cost for talking $g$ minutes is $1 \times g = g$.
The cost for using $mb$ MB of data is $0.50 \times mb$.
The total cost ($C$) is the sum of the call cost and the data cost.

$$C = g + 0.50(mb)$$

a) The expression for the total cost is $\boxed{g + 0.50(mb)}$.

b) What will be the total cost if you talk 30 minutes and use 200 mb of data?
Substitute $g = 30$ and $mb = 200$ into the expression from part (a).

$$C = 30 + 0.50(200)$$ $$C = 30 + 100$$ $$C = 130$$

b) The total cost will be $\boxed{\text{K130}}$.