First, multiply by 3 on both sides:

Divide by 7:

So,
k = 9
The formula for the area of a trapezoid is A = a+b/2 * h. So just plug in the dimensions.
A = 5 + 3/2 * 5
A = 8/2 * 5
A = 4 * 5
A = 20 units²
I hope this helps love! :)
If 1/6 of the pan was left and there were 2 pieces left you just need to set 1/6 equal to 2/some number, this allows you to say that 1/6=2/x --> x/6=2-->x=12.
My explanation might be a little poor since this becomes fairly fundamental later on but hopefully it helps.
Answer:
The blue dot represents the absolute value of the number occupied by red dot.