Gil,eva e lisa colecionam chaveiros.gil tem 1 chaveiro a mais que eva,e eva tem 1 a mais que lisa.juntose eles tem 81 chaveiros.quantos chaveiros cada um tem?

While writing inequalities we should know about symbols a>b means a is greater than b a<b means a is less than b so here we have to write difference between t and 7= t-7 given t-7 is greater than 10 so t-7>10 and t-7 is less than 20 so t-7<20 combining above two we get 10<t-7<20, 17 < t < 27