Can someone solve this equation?

2.6x + ? = 2x

The lengths of all sides of a triangle are integers when measured in decimeters. one of the sides has length of 1 dm and another of 3 dm. find the perimeter of the triangle.'

The two square pyramids are similar. find the total volume of both pyramids if the ratio of their surface areas is 9/16

87.5% , 100% , 83.33 , 93.33% , 100% , 82.5% are all the academic points i've gotten this quarter. what's my final grade?