You have the following summation:
48.1 + 29.7 + 11.8
In order to sum the previous expression by using front-end estimation, you first sum the integers first, just as follow:
48 + 29 + 11 = 88
Next, you look at the decimal and approximate them to the nearest whole number:
0.1 + 0.7 + 0.8
0.1 + 0.7 = 0.8 which is approximatley 1
Then
0.1 + 0.7 + 0.8 = 0.8 + 0.8 = 1 + 1 = 2
Finally, you sum the two contributions:
88 + 2 = 90
Then, by using the front-end estimation you have:
48.1 + 29.7 + 11.8 = 90
