Step-by-step explanation:
x = number of trucks with 16 tonnes capacity
y = number of trucks with 6 tonnes capacity
x + y = 11
16x + 6y = 126
the first equation gives us
x = -y + 11
and we use that in equation 2 :
16(-y + 11) + 6y = 126
-16y + 176 + 6y = 126
-10y = -50
10y = 50
y = 5
x = -y + 11 = -5 + 11 = 6
the number of 16 tonne trucks was 6.
