Determine the operations represented by A, B, and C.

We are given two equations:

1. $30 \text{ A } 10 \text{ B } 30 \text{ C } 10 = 37$
2. $45 \text{ A } 15 \text{ B } 18 \text{ C } 9 = 58$

Let's test common mathematical operations. If we assume:
A = Addition (+)
B = Subtraction (-)
C = Division (÷)

Let's check the first equation:

$$30 + 10 - 30 \div 10$$

Following the order of operations (BODMAS/PEMDAS):
First, division: $30 \div 10 = 3$
Then, addition and subtraction from left to right:
$30 + 10 - 3 = 40 - 3 = 37$
This matches the given result for the first equation.

Now, let's check the second equation with the same operations:

$$45 + 15 - 18 \div 9$$

First, division: $18 \div 9 = 2$
Then, addition and subtraction from left to right:
$45 + 15 - 2 = 60 - 2 = 58$
This also matches the given result for the second equation.

So, the operations are:
A = +
B = -
C = ÷

The target expression is:
$64 \text{ A } 34 \text{ B } 50 \text{ C } 5 = ?$

Substitute the operations:

$$64 + 34 - 50 \div 5$$

Following the order of operations:
First, perform the division:

$$50 \div 5 = 10$$

The expression becomes:

$$64 + 34 - 10$$

Next, perform the addition:

$$64 + 34 = 98$$

The expression becomes:

$$98 - 10$$

Finally, perform the subtraction:

$$98 - 10 = 88$$

The value of the expression is 88.

Comparing with the given options:

1. 87
2. 88
3. 90
4. 80

The calculated value matches option 2.

The final answer is $\text{88}$