If $a: b = 3: 5$ and $b: c = 4: 7,$ then $a: c$ is equal to

Before a war,the ratio of tanks to planes in an army was $5:3$. During the war,$1000$ tanks were destroyed and $800$ planes were destroyed. The ratio of tanks to planes became $2:1$. What is the number of tanks after the war?

If $18: x = x: 8$,then $x$ is equal to

An alloy of copper and zinc is taken in the ratio $1: 2$,and another alloy of the same metals is taken in the ratio of $2: 3$. How many parts of the two alloys must be taken to obtain a new alloy consisting of copper and zinc that are in the ratio $3: 5$?

One year ago,the ratio of Ramu's and Somu's ages was $6:7$ respectively. Four years hence,their ratio will become $7:8$. How old (in years) is Somu?

In a family,the ratio of expenses to savings is $5:3$. If the expenses increase by $60\%$ and the income increases by $25\%$,the savings decrease by $Rs. 3500$. Find the increased income (in $Rs.$) of the family.