Answer:
100
Step-by-step explanation:
Black keys 5 10 100
Total keys
Black keys + white keys = 12 24 240
Multiply 2nd equation by 3 and add to first
9x-3y=-2
<u>-9x+3y=-9 +</u>
0x+0y=-7
0=-7
false
no solution
these lines aer paraalell so no solution
The Solution.
Representing the problem in a diagram, we have
By formula,

In this case,

Substituting these values in the formula above, we get

Clearing the bracket, we get



Dividing both sides by 2, we get

Therefore, the correct answer is option C.