First, expand the terms in parenthesis by multiplying each term within the parenthesis by the term outside the parenthesis:
#color(red)(3)(b - 5) < -2b#
#(color(red)(3) xx b) - (color(red)(3) xx 5) < -2b#
#3b - 15 < -2b#
Next, add #color(red)(15)# and #color(blue)(2b)# to each side of the inequality to isolate the #b# term while the keeping the inequality balanced:
#color(blue)(2b) + 3b - 15 + color(red)(15) < color(blue)(2b) - 2b + color(red)(15)#
#(color(blue)(2) + 3)b - 0 < 0 + color(red)(15)#
#5b < 15#
Now, divide each side of the inequality by #color(red)(5)# to solve for #b# while keeping the inequality balanced:
#(5b)/color(red)(5) < 15/color(red)(5)#
#(color(red)(cancel(color(black)(5)))b)/cancel(color(red)(5)) < 3#
#b < 3#