1) (-0.75 + 1/2) ÷ 4/3
First, let's simplify the expression inside the parentheses:
-0.75 + 1/2 = -3/4 + 1/2 = -3/4 + 2/4 = -1/4

Now we have:
(-1/4) ÷ 4/3

To divide by a fraction, we can multiply by its reciprocal:
(-1/4) * (3/4) = -3/16

So, (-0.75 + 1/2) ÷ 4/3 = -3/16

2) 7.5 - 1 and 3/4 - 6 and 2/5
First, let's convert the mixed numbers to improper fractions:
7.5 = 7 5/10 = 7 1/2 = 15/2
6 and 2/5 = 6 + 2/5 = 30/5 + 2/5 = 32/5

Now we have:
15/2 - 1 and 3/4 - 32/5

To subtract mixed numbers, we need to find a common denominator:
15/2 - 1 and 3/4 = 15/2 - 4/4 - 3/4 = 15/2 - 7/4 = 30/4 - 14/4 = 16/4 = 4

Now we have:
4 - 32/5

To subtract fractions, we need a common denominator:
4 = 20/5

Now we have:
20/5 - 32/5 = -12/5

So, 7.5 - 1 and 3/4 - 6 and 2/5 = -12/5