Simple Algebra skills...
(Minus X Minus) = positive number. eg. -2x-10 = 20
(Minus X Plus) = negative number. eg. -2x10 = -20
(Plus X Minus) = negative number.
(Plus X Plus) = positive number. eg. 2x10 = 20
To answer your question. (-3)(-6) is 18.
Brackets or parenthesises in maths, placed next to each other means Times