Elementary Geometry for College Students (5th Edition)

a.) 90$^{\circ}$-x$^{\circ}$ b.) 102$^{\circ}$-3x$^{\circ}$ c.) 90$^{\circ}$-2x$^{\circ}$-5y$^{\circ}$
To find the second of two complimentary angles you subtract the value of the given angle from 90$^{\circ}$.