ANSWERS
(a) 7.61 USD
(b) 1247.98 MXN
Step-by-step explanation
We know that on March 8, 2017, 1 USD was worth 19.61 MXN.
(a) To find how many dollars was 149.23 MXN worth on that date, we have to divide this amount by 19.61,

Hence, 149.23 Mexican pesos were worth 7.61 US dollars.
(b) Now, to find how many Mexican pesos were 63.64 USD worth on that date, we have to multiply it by 19.61 instead,

Hence, 63.64 US dollars were worth 1247.98 Mexican pesos.