Please teach me how to do this?

Apatient is to be given 35 milligrams of demerol every 4 hours. you have demerol 50 milligrams/milliliter in stock. how many milliliters should be given per dose?

3x + 4y = 5 x- 3y = -7 solve by substitution

He trapezoid is composed of a rectangle and two triangles. what is the area of the rectangle? what is the total area of the triangles? what is the area of the trapezoid? ? a) 42 cm2; 27 cm2; 69 cm 2 b) 54 cm2; 27 cm2; 81 cm 2 c) 108 cm2; 27 cm2; 135 cm 2 d) 108 cm2; 13.5 cm2; 121.5 cm 2