In a group of 26 pupils, 3 play the flute only. 5 play the piano only.
7 play neither instrument.
How many pupils play both instruments?

Here is a Venn diagram:

First put in the value of X into all the X's. So 10(3) times 10(3) minus 7 times -12. Then simplify, 10(3)= 30. then your equation would turn out like this 30×30×-7×-12. After that multiply first then Subtract, 30×30=90 and -7×-12=84. then you have 90+84 left and then add them together and you get 174.