Question

Hola me ayudan con esto porfa

Answer 1

A: number of tables with 6 seats
b: number of tables with 4 seats

so when cafe is full 
ax6 + bx4 = 100 seats
then
3a + 2b = 50 seats....    (i)

also 
a + b = 20 tables 
a + b = 20
a = 20-b ...(ii)

(ii) in (i)

3(20-b)+2b=50
60-3b+2b=50
b=10

how a+b=20

then a = 10

there are 10 tables of 6 seats and 10 tables of 4 seats