Intermediate Algebra by AoPS
Intermediate Algebra is an AOPS(Art of Problem Solving) book. This book is written by Richard Rusczyk and Matthew Crawford. Mr. Crawford is the founder and CEO of MIST Academy. Some of his key Math Competition achievements are...
National MathCounts written test champion in 7th grade (perfect score of 46) and second place in 8th grade (score of 44)! Twice perfect scorer on the AHSME! Perfect score(All correct) on the AIME in 9th grade! Invited to the Mathematical Olympiad Summer Program 3 times! Part of top 4 Putnam team! Youngest winner of National Mu Alpha Theta convention! The one and only 5 time winner of the Alabama State Written Examination (Algebra II/Trig once, Comprehensive four times)! Two times he was ARML high scorers (tie-breaker) and Zachary Sobol Award winner (source:https://artofproblemsolving.com/wiki/index.php/Mathew_Crawford).
Plus Mr. Crawford also was first AOPS employee and author of Introduction to Number Theory.
While Mr. Rusczyk is the founder of AOPS(without him you'd not be here!). Some key achievements of him are that he once was MATHCOUNTS participants in Nationals, perfect score of AIME, USAMO winner, and participant of Math Olympiad Summer Program. Along with this Mr. Rusczyk has been coauthor of Art of Problem Solving: Volumes 1 & 2, Introduction to Prealgebra, and Intermediate Algebra(which you all know). While he alone wrote Introduction to Algebra and Introduction to Precalculus(Source: Back of Introduction to Geometry)
From this you guys can see these both are very intelligent people meaning this book would be really helpful struggling or not struggling at Math. This book explains very hard concepts in a very simple way. The difficulty rating of this is 2.5-7 depending from Chapter to Chapter(see https://artofproblemsolving.com/wiki/index.php/AoPS_Wiki:Competition_ratings#Introduction_to_Geometry_by_AoPS)
Besides, including concepts this piece of text has advanced topics required for success on Prestigious Competitions(e.g. AMC, AIME)