B1. The sum of two numbers is 90 . $40 \%$ of the first number is 15 more than $30 \%$ of the second number.
Find the two numbers.
SolUTION
Let the first number be $a$. Then the second number is $90-a$. Therefore $0.4 a=0.3(90-a)+15$. Expanding the bracket gives $0.4 a=27-0.3 a+15$. Multiplying the equation by 10 gives $4 a=270-3 a+150$.

After rearrangement we have $7 a=420$. Therefore $a=60$ and the two numbers are 60 and 30 .