几道数学题：（简便运算）10.1×99-9.9 (解方程)2.3(X+5)=52.9 1.15X—2.3=12.7

简便运算
10.1×99-9.9
=101×9.9-9.9
=(101-1)×9.9
=100×9.9
=990
(解方程)
2.3(X+5)=52.9
2.3X+11.5=52.9
2.3X =52.9-11.5
2.3X =41.4
X=18
1.15X—2.3=12.7
1.15X=12.7+2.3
1.15X=15
X约 =13.04