Substitution

This week in maths I have ben working on substitution. Substitution in maths means replacing a number with a letter. Kinda of like in rugby, number 9 comes off and is replaced by number 21.
Here is some of the practice work I have been doing

2. Substitute the values given in the following formulae to find the value of the unknown variable. Make sure that the correct units are given.

(a)	V = d/t	find the velocity v, when d = 80 km and t = 4 hours
(b)	A = l w	find the area A of a rectangle , when l = 20 cm and w = 5 cm
(c)	C = 2πr	find the circumference C, when π = 3 and r = 8 cm
(d)	V = 1/3Ah	find the volume V, when A = 21 cm2 and h = 6 cm