b. \(\left(2\frac{1}{3}+3\frac{1}{2}\right):\left(-4\frac{1}{6}+3\frac{1}{7}\right)+7\frac{1}{2}\)

\(\left(\frac{7}{3}+\frac{7}{2}\right):\left(-\frac{25}{6}+\frac{22}{7}\right)+\frac{15}{2}\)

\(\frac{35}{6}:-\frac{43}{42}+\frac{15}{2}\)

\(-\frac{245}{43}+\frac{15}{2}=\frac{155}{86}\)

10 giờ 45 phút

180 km

b.\(3x+1=3x+3\)

\(0x=2\)

\(x=\varnothing\)

a. \(7\left(x+3\right)=5\left(x+7\right)\)

\(7x+21=5x+35\)

\(2x=14\)

\(x=7\)

d.\(-7:4\frac{2}{3}=-\frac{3}{2}\)

\(0,9:\left(-0,5\right)=-\frac{9}{5}\)

\(\Rightarrow-7:4\frac{2}{3}\ne0,9:\left(-0,5\right)\)

=> k lập ddc tỉ lệ thức

c.\(6,51:15,19=\frac{651}{1519}=\frac{3}{7}\)

\(3:7=\frac{3}{7}\)

\(\Rightarrow6,51:15,19=3:7\)

=> lập đc tỉ lệ thức

b.\(39\frac{3}{10}:52\frac{2}{5}=\frac{393}{10}:\frac{262}{5}=\frac{3}{4}\)

\(2,1:3,5=\frac{21}{35}=\frac{3}{5}\)

\(\Rightarrow39\frac{3}{10}:52\frac{2}{5}\ne2,1:3,5\)

=> k lập đc tỉ lệ thức

a.\(3,5:5,25=\frac{350}{525}=\frac{2}{3}\)

\(14:21=\frac{14}{21}=\frac{2}{3}\)

\(\Rightarrow3,5:5,25=14:21\)

=> lập đc tỉ lệ thức

\(4x-20=2^{15}:2^{12}\)

\(4x-20=2^3\)

\(4x=28\)

\(x=7\)

v2/v1=t1/t2 =7/4 

v2-v1= 3km/h

v1= 4km/h

v2= 7km/h