Think of FOIL... First Outer Inner Last
Multiply the first of both parentheses -2a times 2a= -4a^2
Now able to eliminate the first two
Now “O” outer ends of the parentheses which is multiplying-2a and -b to = 2ab keep that in mind
“I” inner of the parentheses which are 3b times 2a to =6ab
Keep that in mind
“L” for last of the parentheses being 3b times -b to = -3b^2
Now we have -4a^2, 2ab, 6ab, and -3b^2.
Combine the like terms which are 2ab and 6ab to = 8ab
Final answer being -4a^2+8ab-3b^2.