Use the given information to set up an equation and solve for the width.

Perimeter	=	length	+	width	+	length	+	width
50 ft	=	15 ft	+	width	+	15 ft	+	width
50 ft	=	15 ft	+	15 ft	+	width	+	width
50 ft	=	30 ft			+	width	+	width
50 ft	=	30 ft			+	10 ft	+	10 ft

Perimeter	=	2	×	length	+	2	×	width
50 ft	=	2	×	15 ft	+	2	×	width
50 ft	=	30 ft			+	2	×	width
50 ft	=	30 ft			+	2	×	10 ft

The width of the rectangle is 10 feet.