Question

144:(15n-3n)=12
143:(5x+6x)=13​

Answer 1

$144:(15n-3n)=12 \\ 144 \div 12n = 12 \\ \frac{12}{n} = 12 \\ n = 1$

$143:(5x+6x)=13 \\ 143 \div 11x = 13 \\ \frac{13}{x} = 13 \\ 13x = 13 \\ x = 1$

Удачи!