12 times the quantity 15 minus a number (d)....
12(15 - d) <== ur expression
Let x = questions with 2 points and y = questions with 4 points;
We solve the equation: x + y = 40 and 2x + 4y = 100;
Then, x = 40 - y;
2( 40 - y ) + 4y = 100;
80 - 2y + 4y = 100;
80 + 2y = 100;
2y = 20;
y = 10;
x = 40 - 10;
x = 30;
