Let the unknown percentage be #x# giving:
#x%xx7.2=45#
The % symbol is like a unit of measurement but one that is worth #1/100# so:
#color(green)(color(red)(x%)xx7.2=45 color(white)("d") ->color(white)("d")[color(red)(x xx1/100)]xx7.2=45)#
#color(white)("ddddddddddddd")->color(white)("dddd")color(green)(color(red)(x/100)color(white)("ddd")xx7.2=45)#
Divide both sides by #7.2# ('gets rid' of it from the left)
#x/100=45/7.2#
Multiply both sides by 100 ('gets rid' of it from the left)
#x=100xx45/7.2#
#x = 625#
But this id the numerator of a percentage so we have:
#625/100color(white)("d")->color(white)("d")625color(white)("d.")ubrace(xx1/100)#
#color(white)("dddddddddddd.dd")darr#
#color(white)("dddd")->color(white)("d")625 color(white)("ddd.")%#
#625%#
