(b) an amount equal to the lesser of the two following amounts:i. 37.5% of the amount of the contributor’s retirement pension, calculated as provided in section 135 and adjusted, where required, in accordance with the third or fourth paragraph of section 132, and
ii. the difference between 1/12 of 25% of the average of the Maximum Pensionable Earnings for the year in which the surviving spouse first became entitled to a retirement pension or to a surviving spouse’s retirement pension, having become entitled to the other such pension, and for each of the two preceding years, and the amount of the surviving spouse’s pension.