We have a "rectangular" double loop, meaning that both loops go to completion.
So there are 3*4=12 executions of t:=t+ij.
Assuming two operatiions per execution of the innermost loop, (i.e. ignoring the implied additions in increment of subscripts), we have 12*2=24 operations in all.
Here the number of operations (+ or *) is exactly known (=24).
Big-O estimates are used for cases with a varying scale of operations, governed by a variable (usually n) to indicate the sensitivity of the number of operations relative to a change in the size of n.
Here we do not have a scale, nor n is defined. The number of operations is constant and known at 24. So a variable is required to find the big-O estimate.
I think that the answer is (4,10). hope it helped :)
Step 1 : Simplify both sides
-5(6a+21)=-15
(-5)(6a)+(-5)(21)=-15
-30a-105=-15
Step 2 : Add 105 to both sides
-30a-105+105=-15+105
-30a=90
Step 3 : Divide both sides by -30
-30a=90
—————
-30 -30
a = -3
