a,151​+54​:x=0,7554​:x=43​−46​54​:x=−43​x=54​:(−43​)x=−1516​b,x+21​=1−xx+x=1−21​2x=21​x=21​:2x=41​

 

$a,\genfrac{}{}{0ex}{}{2}{3}.\genfrac{}{}{0ex}{}{5}{4}-\genfrac{}{}{0ex}{}{3}{4}.\genfrac{}{}{0ex}{}{2}{3}=\genfrac{}{}{0ex}{}{2}{3}.\left(\genfrac{}{}{0ex}{}{5}{4}-\genfrac{}{}{0ex}{}{3}{4}\right)=\genfrac{}{}{0ex}{}{2}{3}.\genfrac{}{}{0ex}{}{2}{4}=\genfrac{}{}{0ex}{}{1}{3}$

$b,2.\left(\genfrac{}{}{0ex}{}{-3}{2}\right)-\genfrac{}{}{0ex}{}{7}{2}=-6.\genfrac{}{}{0ex}{}{1}{2}-7.\genfrac{}{}{0ex}{}{1}{2}=\left(-6-7\right).\genfrac{}{}{0ex}{}{1}{2}=-13.\genfrac{}{}{0ex}{}{1}{2}=\genfrac{}{}{0ex}{}{-13}{2}$

$c,-\genfrac{}{}{0ex}{}{3}{4}.5\genfrac{}{}{0ex}{}{3}{13}-0,75.\genfrac{}{}{0ex}{}{36}{13}=-\genfrac{}{}{0ex}{}{3}{4}.\left(\genfrac{}{}{0ex}{}{68}{13}-\genfrac{}{}{0ex}{}{36}{13}\right)=-\genfrac{}{}{0ex}{}{3}{4}.\genfrac{}{}{0ex}{}{32}{13}=-\genfrac{}{}{0ex}{}{24}{13}$

chu vi mảnh vườn là:
(5,5+3,75).2=37(m)
1/4=0,25m
số khóm hoa cần trồng là:
37:0,25=148(khóm hoa)