$\text{a,15.141+53.15}$
=$\text{(15 x141+53)}$
= $\text{15.194}$
=$\text{2910}$
$\text{b,17.85+15.17-1200}$
=$\text{17 x(85+15)-1200}$
=$\text{17 x 100-1200}$
=$\text{1700-1200}$
$\text{=500}$
c,100:{250:[450-4.125-4.25)]}
=$\text{ 100 : {250:[450 - ( 500 - 100)]} }$
$\text{=100:(250 : (450-400)}$
$\text{=100:(250:50)}$
$\text{=100 :50}$
$\text{=2}$
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