Using the order of operation which states
Expressions in brackets/parentheses are evaluted first, followed by expressions involving orders, division, multiplication, addition and subtraction in that order.
Thus,
1)
thus, 3+(7−5)2×6 = 27
2)
thus, 25(4+4)×2 = 400
3)
thus, 8−6÷2+3×5 = 20
4)
thus, 7×3−15÷5 = 18
5)
thus, 8+2(1+12÷2)2 = 36.