Translate the written expression eighteen less than the product of n and m into a mathematical expression and evaluate it when n = 4 and m = 7.
a) 18 - nm; Value at n = 4, m = 7 is 10.
b) nm - 18; Value at n = 4, m = 7 is 10.
c) 18 + nm; Value at n = 4, m = 7 is 46.
d) nm + 18; Value at n = 4, m = 7 is 46.