Verified Answer :

If the mini horse is 56kg and it's 268kg less than a Shetland pony then a Shetland pony would weigh 56+268=324kg

let
x--------> Shetland pony's weigh
y--------> M
iniature horse's weigh

we know that
\(y=56 kg\)
\(x=268+y \\ x=268+56 \\ x=324 kg\)

the answer is
Shetland pony's weigh is \(324 kg\)