(580:b-25)*90+490=850

Question

(580:b-25)*90+490=850

Answer 1

(580:b-25)*90+490=850

(580:b-25)*90=360

(580:b-25)=360:90

580:b-25=4

580:b=25+4

580:b=29

b=580:29

b=20

Answer 2

(580:b - 25) = 360 / 90;
(580:b - 25 = 40;
580:b = 65;
b = 580 / 65