You will notice that 48°, x, and x lie upon a straight line. The sum of those angles must then be equal to 180°. Which means:
48+x+x=180
48+2x=180
2x=132
x=66°
Lets look at the number. 76.78. In each of the different place holders the number is higher than 5. Lets do some examples. 74 rounded to the nearest whole number is going to be 70. 76 rounded to the whole number will be 80. The .78 in your question also contributes.
Answer: 80
