Adjacent angles in a parallelogram are supplementary

let A, B be the angles adjacent angles of the parallelogram

A + B = 180

the measure of an angle of a parallelogram is 18 degrees less than 5 times the measure of an adjacent angle

A = 5*B - 18

by solving the system of equations

A + B = 180

B = 5*A - 18

we find

A = 33 degrees

B = 147 degrees

click here to see the step by step solution of the system of equations

the interior angles of the parallelogram are 33 degrees and 147 degrees.