Number #11 only : ) is appreciated

2x minus y equals 6, x plus y equals negative 3

In the sixth grade 13 out of 20 students have a dog if there are 152 sixth grade students how many of them have a dog

Luke started a weight-loss program. the first week, he lost x pounds. the second week, he lost pounds less than times the pounds he lost the first week. the third week, he lost 1 pound more than of the pounds he lost the first week. liam started a weight-loss program when luke did. the first week, he lost 1 pound less than times the pounds luke lost the first week. the second week, he lost 4 pounds less than times the pounds luke lost the first week. the third week, he lost pound more than times the pounds luke lost the first week.