(a) 2*1.
Substitute p= 2, q= 1 into the formula
2*1 = 1 - 3*2 = 1 - 6 = -5.
(b) Do (b) exactly in the same way.
(c) Now, when you just know how to handle two-term aggregate,
move forward and calculate (1*2) first.
After that, make the last step.
Having my instructions, you just know what to do and how move forward.