Note that to trigger maths formatting you put a hash at the beginning and end of the maths part. Have a look at

https://socratic.org/help/symbols

#color(green)("If your original equation is different to this then look at how")##color(green)("I solved this one and use the same approach to solve the correct formula")#

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Assumption - the equation is meant to be:

#51/x +11=15/5#

White as:

#51/x+11/1=15/5#

Turn everything upside down so that the #x# is on the top of the fraction (numerator) giving:

#x/51+1/11=15/5#

Subtract #color(red)(1/11)# from both sides so that you end up with just the #x# term on the left of the equals.

#color(green)(x/51+1/11color(red)(-1/11)" "=" "15/5color(red)(-1/11)#

but #1/11-1/11=0#

#color(green)(x/51+0" "=" "15/5-1/11#

Multiply both side by #color(red)(51)# so that you end up with just #x# on the left.

#color(green)(x/51color(red)(xx51)" "=" "32/11color(red)(xx51)#

#color(green)(x xx(color(red)(51))/51" "=" "157 1/11 #

But #51/51=1 and 1xx x=x#

#x=157 1/11#