Find the value of the following algebraic expressions using the indicated constants.
1. 7a + 4; a = 6

2. d + e – f when d = 3, e = 2 and f = -2

3. 10x – 12y + 1; x = 3 and y = 2

4. (m + n)2 – mn, when m = -1 and n = 3

5. x 2y – 6xy + 3x; x = 2 and y = 3