Substitution!

If y = 3, x = 4 and z = 5

Evaluate: y + x

if y = 3, x = 4 and z = 5

evaluate: yx

if y = 3, x = 4 and z = 5

evaluate: yx - 6

if y = 3, x = 4 and z = 5

evaluate: yx + 3z

if a = -2, b = -4 and c = 3

evaluate: a - b

if a = -2, b = -4 and c = 3

evaluate: abc