This information alone is not enough as the angles between the sides will greatly vary the amount of square footage inside. I think you may need to break up the plot plan into squares and count them up.

I DO NOT KNOW HOW TO BREAK UP, CAN YOU TELL HOW OR IS THIS DIFFICULT?

I believe your lot size to be 19008 Sqft or roughly .43/acre (a full acre consists on 43,560sqft). for something like a pie shaped lot you just take an average of the sides then multiply them as 2 numbers instead or 4 (avg of front 119ft and back 97ft is 108ft and avg of left side 177ft and right side 175ft is 176ft. so all you have to do is multiply 108X176 and there you go.