Let x be the number of operators and y be the number of laborers.

Thirty-five people were hired so:

\(\displaystyle{x}+{y}={35}{\left({1}\right)}\)

The payroll was $3950 so:

\(\displaystyle{140}{x}+{90}{y}={3950}{\left({2}\right)}\)

Solve for yy using (1) to obtain (3):

\(\displaystyle{y}={35}−{x}{\left({3}\right)}\)

Substitute (3) to (2) and solve for x:

\(\displaystyle{140}{x}+{90}{\left({35}−{x}\right)}={3950}\)

\(\displaystyle{140}{x}+{3150}−{90}{x}={3950}\)

\(\displaystyle{50}{x}+{3150}={3950}\)

\(\displaystyle{50}{x}={800}\)

\(\displaystyle{x}={16}\)

Solve for y using (3):

\(\displaystyle{y}={35}−{16}\)

\(\displaystyle{y}={19}\)

So, there were 16 operators and 19 laborers.

Thirty-five people were hired so:

\(\displaystyle{x}+{y}={35}{\left({1}\right)}\)

The payroll was $3950 so:

\(\displaystyle{140}{x}+{90}{y}={3950}{\left({2}\right)}\)

Solve for yy using (1) to obtain (3):

\(\displaystyle{y}={35}−{x}{\left({3}\right)}\)

Substitute (3) to (2) and solve for x:

\(\displaystyle{140}{x}+{90}{\left({35}−{x}\right)}={3950}\)

\(\displaystyle{140}{x}+{3150}−{90}{x}={3950}\)

\(\displaystyle{50}{x}+{3150}={3950}\)

\(\displaystyle{50}{x}={800}\)

\(\displaystyle{x}={16}\)

Solve for y using (3):

\(\displaystyle{y}={35}−{16}\)

\(\displaystyle{y}={19}\)

So, there were 16 operators and 19 laborers.